What Is the Autonomic Nervous System? Sympathetic vs Parasympathetic Functions, Stress, Menopause & Lifestyle

When you search for information about symptoms such as feeling unusually tired, having difficulty sleeping, or experiencing a racing heartbeat when nervous, you may often come across the term “autonomic nervous system”.

Expressions such as “balance your autonomic nervous system” or “your autonomic nervous system is out of balance” are also commonly used on television and online.

But what exactly does the autonomic nervous system do?

And when you are not feeling well, should every symptom really be attributed to an “autonomic imbalance”?

The autonomic nervous system regulates many of the body’s functions that continue without us consciously thinking about them, including heart rate, blood pressure, body temperature, digestion and sweating.

Its two major divisions are the sympathetic and parasympathetic nervous systems.

Neither one is simply “good” or “bad”. Both have important roles during activity, rest and different situations throughout the day.

Symptoms such as dizziness, headaches, palpitations, fatigue and difficulty sleeping can also have many causes unrelated to the autonomic nervous system.

For this reason, it is important not to assume from symptoms alone that your autonomic nervous system is “out of balance”. Medical advice may be appropriate when symptoms persist or cause concern.

This article explains the basics of the autonomic nervous system, the differences between the sympathetic and parasympathetic systems, what people mean when they talk about “autonomic imbalance”, autonomic dysfunction, menopause, and everyday lifestyle factors worth considering.

What is the autonomic nervous system?

Many functions in our bodies continue constantly without conscious effort.

Even while we sleep, the heart continues to beat, breathing continues and body temperature is maintained within an appropriate range.

After we eat, digestion begins. When we become hot, we sweat. Many bodily functions are continuously adjusted according to our physical condition and the environment around us.

The autonomic nervous system plays an important role in regulating these processes.

A nervous system you cannot directly control by willpower alone

When you move your hand or walk, you can intentionally activate muscles by deciding to move.

Many functions involving the autonomic nervous system are different. You cannot simply decide, “I will set my heart rate to this number,” “I will start digestion now,” or “I will stop sweating.”

The autonomic nervous system regulates various functions in response to the body and its surroundings without requiring conscious control.

Some of the main functions influenced by the autonomic nervous system include:

• Heart rate regulation
• Blood pressure regulation
• Body temperature regulation
• Sweating
• Digestive function
• Urination and bowel function
• Pupil size

In other words, the autonomic nervous system is not connected to only one organ. It is a nervous system that helps support essential functions throughout many parts of the body.

You cannot freely “control” your autonomic nervous system

Health information sometimes uses expressions such as “controlling the autonomic nervous system”.

However, the autonomic nervous system itself cannot be freely switched or directly controlled simply through conscious thought.

At the same time, everyday factors such as sleep, physical activity, rest, diet and how we manage stress can influence our overall physical and mental condition.

Rather than thinking in terms of directly controlling your nerves, it may be more useful to focus on creating everyday conditions that help your body respond appropriately to different situations.

How are the sympathetic and parasympathetic nervous systems different?

The autonomic nervous system is broadly divided into:

• The sympathetic nervous system
• The parasympathetic nervous system

In health and wellness information, these are often compared to:

“Sympathetic nervous system = accelerator”
“Parasympathetic nervous system = brake”

This can be a useful way to visualise the difference, but the way the body actually works is more complex.

The sympathetic and parasympathetic systems each contribute to regulating different functions according to what the body needs at the time.

The sympathetic nervous system is involved in activity and responses to demanding situations

The sympathetic nervous system plays an important role during activity and when the body needs to respond to tension, danger or other demanding situations.

For example, during an emergency response:

• Heart rate may increase
• The force of heart contractions may increase
• The airways may widen
• Sweating may increase
• Some digestive activity may decrease temporarily

These responses are commonly associated with the “fight-or-flight response”, a natural mechanism that helps the body respond to demanding or potentially dangerous situations.

This means that sympathetic nervous system activity is not something that should automatically be considered “bad”.

It also plays an important role when working, exercising, concentrating and responding quickly to the environment.

The parasympathetic nervous system is involved in rest and digestion

The parasympathetic nervous system is particularly involved during rest and with functions such as eating and digestion, helping the body maintain itself while conserving energy.

Its roles include:

• Helping reduce heart rate
• Supporting digestive activity and secretions
• Contributing to urinary and bowel functions

This is why the parasympathetic nervous system is often associated with relaxation.

It is not a matter of “sympathetic is bad and parasympathetic is good”

This is an important point when trying to understand the autonomic nervous system.

You may see claims suggesting that modern stress causes excessive sympathetic activity and that the goal should therefore be to make the parasympathetic system as dominant as possible.

However, both systems are necessary for everyday life.

Increasing heart rate during exercise or responding quickly to danger can be important, just as digestion and rest are important.

Rather than trying to keep the parasympathetic system dominant at all times, it is more useful to understand that the body needs to respond appropriately to changing situations.

When might you feel that your autonomic nervous system is “out of balance”?

It is common to hear people say, “I feel like my autonomic nervous system is out of balance lately.”

This feeling may occur during periods when:

• Life has been unusually busy
• You are experiencing psychological stress
• You are not getting enough sleep
• Your daily schedule has become irregular
• Your work or living environment has changed significantly
• Physical or mental fatigue has been continuing

When tiredness, difficulty sleeping, digestive discomfort, palpitations or sweating occur alongside these situations, some people may wonder whether their autonomic nervous system is responsible.

Feeling stress is not automatically abnormal

When faced with stress, the body produces various responses that help it deal with the situation.

For example, before an important meeting or during a nervous situation, your heart may beat faster or your palms may become sweaty.

These reactions themselves are part of the body’s natural response mechanisms.

Therefore, sympathetic nervous system activity does not automatically mean that the autonomic nervous system is “out of balance”.

It is too simplistic to say “sympathetic during the day, parasympathetic at night”

You may sometimes hear that the sympathetic nervous system works during the day while the parasympathetic system works at night.

In reality, both systems remain active throughout the day, with their activity changing according to circumstances.

For example, parasympathetic functions are involved during meals and rest even in the daytime, while sympathetic activity may also change during the night depending on the body’s condition.

The autonomic nervous system does not work like a simple switch where one side is completely on while the other is completely off.

Do not automatically blame every symptom on the autonomic nervous system

This is particularly important.

When searching online about the autonomic nervous system, you may see a very wide range of symptoms listed, including:

• Headaches
• Dizziness
• Palpitations
• Fatigue
• Sweating
• Digestive discomfort
• Difficulty sleeping
• Feelings of anxiety

However, these symptoms can also occur for many reasons unrelated to the autonomic nervous system.

Possible causes may include anaemia, thyroid disorders, cardiovascular conditions, infections, sleep disorders, inner-ear problems, medication effects and mental health conditions.

For this reason, avoid assuming that “the autonomic nervous system must be the cause” simply because you have one or more of these symptoms.

If symptoms persist or interfere with everyday life, it is important to have the cause appropriately assessed by a healthcare professional.

What is autonomic dysfunction?

You may also encounter the term “autonomic dysfunction” or similar expressions used to describe symptoms associated with the autonomic nervous system.

In Japan, the term “autonomic nervous system imbalance” is sometimes used to describe various symptoms experienced when no clear physical disease has been identified and the symptoms are thought to involve autonomic nervous system function.

Symptoms commonly discussed in this context may include:

• General fatigue
• Dizziness
• Headaches
• Palpitations

Do not think of it only as “a disease caused by an imbalance between the sympathetic and parasympathetic systems”

Autonomic dysfunction is sometimes simplified as:

“A condition that occurs when the balance between the sympathetic and parasympathetic nervous systems is disrupted.”

However, real-world symptoms are rarely that simple.

Similar symptoms can have very different causes between individuals, including physical illness, medication effects, sleep problems, psychological factors and lifestyle or environmental changes.

This is why it is important not to decide in advance that autonomic dysfunction is the cause. Other possible medical causes should be considered and, when appropriate, ruled out.

Because the symptoms are broad, be careful with self-diagnosis

The range of symptoms associated with autonomic dysfunction can be broad, and no single symptom is enough to make a diagnosis.

If you continue to feel unwell, avoid relying only on self-diagnosis and consider seeking appropriate medical advice based on your symptoms.

If you suddenly develop severe symptoms such as chest pain, severe shortness of breath or fainting, do not simply assume they are related to the autonomic nervous system. Prompt medical assessment is important.

Female hormones, menopause and the autonomic nervous system

When researching women’s health, you may come across explanations such as:

“During menopause, hormonal balance changes and the autonomic nervous system also becomes unbalanced.”

Changes in female hormones and the autonomic nervous system are not completely unrelated. However, the wide range of symptoms experienced during menopause cannot simply be explained as an “autonomic imbalance”.

What is menopause?

In Japan, menopause is generally defined as the approximately ten-year period consisting of the five years before and five years after the final menstrual period.

The timing of menopause varies between individuals, although the average age of menopause among Japanese women is around 50.

During this period, ovarian function gradually declines and levels of oestrogen, one of the main female sex hormones, fluctuate and decrease.

Some people may experience changes such as:

• Hot flushes
• Increased sweating
• Dizziness
• Palpitations
• Fatigue
• Headaches or shoulder discomfort
• Difficulty sleeping
• Irritability or low mood

However, these changes do not occur in exactly the same way for everyone, and their severity varies considerably.

Menopausal symptoms are not determined by hormones alone

It is easy to assume that all menopausal symptoms occur simply because oestrogen levels decline, but the situation is more complex.

In addition to hormonal changes, contributing factors may include:

• Physical changes associated with ageing
• Sleep and lifestyle habits
• Psychological factors
• Work circumstances
• Family environment
• Relationships and other social factors

These factors may interact in different ways.

For this reason, it is important not to explain everything with the simple idea that “hormonal imbalance caused autonomic imbalance”.

Brain function is involved in both autonomic and hormonal regulation

Areas of the brain including the hypothalamus are involved in both autonomic nervous system regulation and hormone-related processes.

The hypothalamus contributes to the regulation of the autonomic nervous system, endocrine functions, body temperature and other physiological processes.

For this reason, hormonal changes during menopause may occur alongside symptoms such as hot flushes and sweating that also involve autonomic nervous system pathways.

However, this does not mean that menopausal symptoms can simply be explained as the result of an autonomic imbalance.

Seek medical advice when symptoms interfere with everyday life

Many different symptoms may occur during menopause. When symptoms become severe enough to interfere significantly with everyday life, medical assessment may be appropriate.

Treatment may include lifestyle adjustments and, depending on the individual, options such as hormone replacement therapy (HRT), traditional medicines or other medications.

It is also possible for symptoms thought to be related to menopause to have another underlying medical cause.

If symptoms are persistent or difficult to manage, avoid simply assuming that they are “because of age” or “because of the autonomic nervous system”, and consider consulting a doctor or gynaecologist.

Everyday lifestyle habits to consider

The autonomic nervous system cannot be directly controlled by willpower alone.

For this reason, there is no need to rely on claims such as:

“This will make your parasympathetic nervous system dominant.”
“This food will balance your autonomic nervous system.”

Instead, focus on maintaining basic lifestyle habits that support overall physical and mental wellbeing, including sleep, physical activity, diet and rest.

Consider your overall sleep routine, not only the number of hours

During busy periods, sleep may become shorter or bedtime and waking time may vary considerably from day to day.

Ongoing sleep deprivation can contribute to daytime sleepiness, difficulty concentrating and feelings of fatigue.

Basic sleep habits to consider include:

• Allowing enough time for the sleep your body needs
• Keeping waking and sleeping times reasonably consistent when possible
• Avoiding work or stimulating activities right up until bedtime
• Creating an environment that makes it easier to sleep comfortably

There is no single universal time window during which everyone must sleep in order to “balance the autonomic nervous system”.

Include appropriate physical activity

Movement and physical activity are basic components of maintaining general health.

This does not necessarily mean performing intense exercise.

Options may include:

• Walking more often
• Doing gentle stretching
• Moving your body within a comfortable range
• Reducing prolonged periods of sitting

Choose activities that suit your physical condition and lifestyle.

Rather than thinking that exercise will “normalise the autonomic nervous system”, consider it as one part of an overall healthy lifestyle that can support fitness, sleep and wellbeing.

Do not search for a special “autonomic nervous system food”

Online information sometimes promotes:

“Foods that balance the autonomic nervous system”
“Nutrients that increase parasympathetic activity”

However, eating one particular food or nutrient does not automatically place the autonomic nervous system into an ideal state.

A balanced everyday diet can include:

• Staple carbohydrate foods
• Protein-containing foods
• Vegetables and fruit
• Sources of vitamins and minerals from a variety of foods

The basic principle is to consider the overall balance and variety of your diet.

Supplements should also not be regarded as products that can, by themselves, treat autonomic symptoms or directly regulate the sympathetic and parasympathetic nervous systems.

Do not rely too heavily on alcohol to help you sleep

Alcohol can make some people feel sleepy, so it is sometimes used as a way to fall asleep more easily.

However, alcohol can affect the quality and structure of sleep.

If the amount you drink is increasing because you are using alcohol to sleep, or you feel unable to sleep without it, this is worth paying attention to.

If heavy drinking continues, consider discussing it with an appropriate healthcare professional rather than trying to manage the situation alone.

Rather than trying to eliminate all stress, notice changes in yourself

Completely eliminating stress from everyday life is unrealistic.

Work, family responsibilities, relationships, moving house, changing jobs and other major life changes can all place demands on us. Even positive changes can sometimes feel stressful.

It can be useful to notice questions such as:

• Am I sleeping well?
• Am I eating normally?
• Does fatigue seem harder to recover from?
• Do I feel that I have less emotional breathing room?
• Is my work or everyday life being affected?

Recognising changes in your own condition can be an important part of everyday health management.

Rest and relaxation do not need to be treated as techniques for “controlling” your autonomic nervous system

Bathing, listening to music, reading, gentle exercise and slow breathing can all be enjoyable ways to rest or take a break.

However, there is no need to create rigid rules such as:

“This breathing method increases parasympathetic activity by a certain amount.”
“A specific number of minutes in the bath will balance your autonomic nervous system.”

Instead, find ways to rest and unwind that feel comfortable and sustainable for you.

When persistent symptoms should be medically assessed

Headaches, dizziness, palpitations, fatigue, insomnia and digestive symptoms can have many causes other than the autonomic nervous system.

If symptoms persist, avoid assuming that they are simply caused by “stress” or “autonomic imbalance”. Finding the underlying cause is important.

Symptoms that may warrant earlier medical attention

Consider seeking medical advice if you experience symptoms such as:

• Repeated or prolonged palpitations
• Severe or persistent dizziness or unsteadiness
• Fainting or episodes where you feel you may lose consciousness
• Chest pain or significant shortness of breath
• A sudden severe headache
• Sudden weakness, difficulty moving a limb or numbness
• Ongoing insomnia that significantly affects everyday life
• Persistent severe low mood or loss of motivation

These symptoms should be appropriately assessed to determine their cause.

In particular, sudden severe chest pain, severe breathing difficulty, fainting, a sudden intense headache, or sudden weakness on one side of the body may indicate a medical emergency and should be assessed urgently.

The appropriate medical department depends on your symptoms

You may wonder which type of doctor to see if you are concerned about symptoms you think might involve the autonomic nervous system.

The most appropriate department depends on the main symptoms.

For example:

• For palpitations or chest symptoms: general medicine or cardiology
• For dizziness or tinnitus: an ear, nose and throat specialist
• For symptoms that may relate to menopause: gynaecology
• For significant anxiety, persistent low mood or severe sleep problems: mental health or psychosomatic medicine services

If you are unsure where to start, consider speaking with your usual doctor or a general practitioner, who can refer you to an appropriate specialist if necessary.

“No clear cause found” does not mean your symptoms are imaginary

If medical tests do not immediately reveal a clear cause, you may begin to wonder whether the symptoms are “all in your head”.

However, a lack of an immediate diagnosis does not mean that the discomfort or difficulty you are experiencing is not real.

If symptoms continue, it can be helpful to explain their severity, when they occur and how they affect everyday life so that you and your healthcare professional can consider the next appropriate steps.

Summary: do not let the term “autonomic nervous system” explain every symptom

The autonomic nervous system regulates many functions that continue without conscious effort, including heart rate, blood pressure, body temperature, sweating and digestion.

Its sympathetic and parasympathetic divisions are both necessary. Neither is simply good or bad, and both contribute to different functions according to the situation.

Key points to remember include:

• Sympathetic nervous system activity is not inherently bad
• The parasympathetic system does not need to dominate all the time
• You cannot freely control the autonomic nervous system through willpower alone
• Do not automatically attribute every physical symptom to the autonomic nervous system
• Sleep, movement, diet and rest are important foundations of everyday health
• Persistent or concerning symptoms should be medically assessed

During menopause, hormonal changes can interact with age-related physical changes, psychological factors, work, family circumstances and other social factors.

Rather than becoming overly focused on the idea that you must “balance your autonomic nervous system”, it may be more helpful to review your sleep, diet, activity, rest and stress levels and continue manageable everyday health habits.

If symptoms persist, worsen or interfere with your daily life, avoid relying solely on self-diagnosis and consider having the underlying cause assessed by a healthcare professional.