The Most Common Biological Causes of Insomnia and the Role of the Sympathetic Nervous System

A woman lying in bed unable to sleep

On this page we will cover the most important biological or internal causes of insomnia. These causes have their origin from within a person, instead of derived from external factors. Three main biological causes are described. These are the genetic predisposition of insomnia, emotional concerns or worrying, and anxiety. We will elaborate on how emotional concerns or worrying often is caused by an overactive sympathetic nervous system. This is the body’s fight or flight mechanism which causes insomnia in multiple ways. Of course there are other factors which can cause insomnia. These are mostly external factors which are covered on the page focused on The External Causes of Insomnia. 

The Genetic Predisposition of Insomnia

Studies indicate that genetics do play a role as insomnia shows a moderate degree of genetic predisposition. Moreover, insomnia has a transmission rate of around 25 to 45 percent from parents to child. In other words, insomnia is moderately heritable with approximately one third of the variance in symptoms being attributable to genetic factors. However, the majority of insomnia cases are being associated with non-genetic causes.

How Psychological Distress Causes Insomnia

The most common biological cause of insomnia is psychological in nature. This is referring to psychological distress which is a major issue for many people. Psychological distress can be caused by either emotional worry or by anxiety, which are two different mental states (see below). Psychological distress (worry and/or anxiety) affects many people and often causes people unable to sleep properly at night, especially in today’s tumultuous climate.

Nowadays, many people in this fast paced and information overloaded world barely have any time to clear their head. They are constantly bombarded with informational triggers. It’s not until their head hits the pillow at night that they have the time to consciously reflect inwardly. This often causes these individuals to overthink certain events or conversations that took place during the day. Furthermore, they worry about what they must face the next day while lying in bed. The emotional worrying late at night disrupts the invitation of calm sleep related brainwaves into the brain. These calming brainwaves are required to fall asleep naturally.

A man sitting outside suffering from anxiety

The Difference Between Worry and Anxiety

Many people nowadays use the terms worry and anxiety interchangeably. Although they are interrelated, they are considered different psychological states. Additionally, they have different implication for health and mental well-being.

When a person worries it is usually about a specific thing with a logical component to it which is grounded in reality. For example, “I worry I will fail my exam next week”. Consequently, in most cases you can get rid of worry by taking a specific action (study for the exam). Feeling anxious however is different. Anxiety is generally vague and cannot always be pinpointed to a specific cause. Many people with anxiety report feeling unsettled without having a specific reason for it. Furthermore, anxiety is often characterized by unrealistic, catastrophic thinking. This makes getting rid of anxiety much more difficult.

Worry is usually only temporary as it can be reduced with problem solving action. While anxiety is more persistent and longstanding. It can significantly impair daily functioning as it can make it difficult to focus and get stuff done. Furthermore, worry largely affects our minds, while anxiety can affect both the mind and the body. This is because anxiety often manifest physically in the body and can cause lightheadedness, hyperventilation and even digestive problems and nausea. These symptoms of anxiety can serve as an early warning signs of serious health conditions such as depression, panic attacks and anxiety disorder. If systems are persistent and regularly disrupt daily activities it is recommend to consult a doctor.

A woman sitting in a chair suffering from mental problems

The Role of the Sympathetic Nervous System in Causing Insomnia

Our body’s automatic nervous system controls the unconscious functions of our body such as our heartbeat, blood pressure, digestion etc. This automatic nervous system consists of two parts, the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system is the fight or flight mechanism of the body which switches on in response to threat or acute stress. The parasympathetic nervous system on the other hand controls our body’s rest and relaxation response. It is responsible for the stimulation of rest-and-digest activities as well as feed and breed activities which occur when the body is at rest.

Research indicates that psychological distress is often caused by an overactive sympathetic nervous system. Consequently, the physiological effects on the body include an increased heart rate, blood flow and metabolic rate. Additionally, this overactive fight or flight mechanism increases brain activation and the release of stress related chemicals such as cortisol. All of these effects are only useful when the body is actually in danger. If this fight or flight mechanism is left on for a prolonged period of time this creates significant health problems such as heart disease. One of the more prominent consequences is insomnia.

An image of a pug wrapped in a blanked looking sad

4 Ways How an Overactive Sympathetic Nervous System Causes Insomnia

  1. Increased Core Body Temperature: The fight-or-flight mechanism raises the metabolic rate of our body. In turn, this increases the core body temperature of the body and the brain. This causes insomnia because in order for our body to initiate sleep it is required to lower our core body temperature by a few degrees.
  2. Increased Hormonal Production: An overactive sympathetic nervous system increases the production of the alertness-promoting hormones in the body. These are cortisol as well as the neurochemicals adrenaline and noradrenaline. All three chemicals raise the heart rate of a person. This elevated cardiac activity prevents our cardiovascular system from calming down. This is required to transition into light and subsequently deep sleep. Additionally, these chemicals also increase core body temperature, further compounding the problem of insomnia.
  3. Increased Psychological Distress: The third factor relates to the inability of insomnia patients to disengage from a pattern of worrisome, reflective brain activity. In healthy people, the parts of the brain related to alertness, inciting emotions (the amygdala) and memory retrospection (the hippocampus) usually calm down when transitioning towards sleep. However, for insomnia patients with an overactive sympathetic nervous system they remain active. Consequently, this prevents the brain from shutting down and switching into sleep mode.
  4. Sleep Fragmentation and Reduced Sleep Quality: The final factor why an overactive sympathetic nervous system facilitates insomnia is related to the quality of sleep once an insomnia patient finally drifts off. Studies indicate that these insomnia patients have less powerful electrical brainwaves during deep NREM sleep. Additionally, they have more fragmented REM sleep characterized by regular brief awakenings. This causes a degraded quality of dream sleep. This is a big issue as REM sleep dreaming is crucial for our health. Consequently, insomnia patients wake up not feeling refreshed and cognitively and/or emotionally impaired throughout the day.

A woman sitting upright in bed visibly worried and tired

How to Reduce Psychological Distress At Night

Luckily, there are a couple of things you can try to reduce overthinking and prevent feelings of worry and anxiety at night:

  • Practicing Mindfulness: As mentioned earlier, our automatic nervous system consists of two parts, the sympathetic nervous system and the parasympathetic nervous system. Only one of these can be active at one point in time. If one is activated the other one is suppressed. Activities such as meditation and yoga help to activate the parasympathetic nervous system. As a result, this contributes to the suppression of the sympathetic nervous system. By activating the relaxation response in our body we can effectively calm our mind, relax our body and drift to sleep naturally and more easily.
  • Implement a Relaxing Bedtime Ritual: Another useful tip is to implement a nightly cooldown ritual in your evening schedule. Before going to bed you should plan a relaxing activity which allows you to unwind such as taking a hot bath, listing to music/podcast, reading a book, practicing yoga/meditation. This will reduce your stress levels and prepare your body and mind for sleep.
  • Turn Off the News: Avoid watching the news, especially in the evening. The news contributes heavily to feelings of psychological distress as most of the time it focusses on negative and anxiety provoking events. You can catch up on news in the morning.
  • Journaling: A great way to clear you head and prevent overthinking late at night is through journaling. If you feel worry or anxiety at night it is recommended to write down all the distracting (and irrational) thoughts that come in your head before going to bed. This will allow you to distance yourself from your worries and anxiety provoking thoughts. This practice can prove to be very effective to decompress and unwind from the stresses of the day.