Unexplained symptoms are worth exploring, but it's important to first speak to your GP and have potential medical causes appropriately investigated. This library is for information only and does not replace medical advice, diagnosis or testing.
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Insomnia describes persistent difficulty falling asleep, staying asleep or returning to sleep after waking, despite having sufficient opportunity to sleep.
It can also involve waking earlier than intended and being unable to fall asleep again.
Insomnia is more than occasionally having a restless night. It can affect how someone feels and functions during the day, contributing to fatigue, irritability, difficulty concentrating or a general sense of exhaustion.
For some people, the main difficulty is falling asleep. Others fall asleep relatively easily but wake repeatedly throughout the night.
Some experience both.
Insomnia can involve:
Lying awake for long periods before falling asleep.
Waking frequently during the night.
Waking in the early hours and being unable to return to sleep.
Feeling physically tired but mentally alert.
Experiencing restless or fragmented sleep.
Becoming increasingly aware of being awake when trying to sleep.
Insomnia can occur independently or alongside conditions such as chronic pain, fibromyalgia, ME/CFS, Long COVID, anxiety disorders, hormonal changes and other illnesses.
It may be short-lived, recurring or persistent over months or years.
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Sleep is regulated by several interacting processes involving the brain, nervous system, hormones and internal biological rhythms.
These systems help determine when we feel sleepy, how easily we fall asleep and how well sleep is maintained throughout the night.
Insomnia can develop when the processes supporting sleep are disrupted or when the systems promoting wakefulness remain unusually active.
Sleep Pressure and the Body Clock
Two important processes influence when we sleep.
Sleep pressure builds during wakefulness, increasing the drive to sleep the longer someone remains awake. A chemical called adenosine is involved in this process.
The circadian rhythm is the body's internal timing system, which helps coordinate sleep, alertness, temperature and hormone release across approximately 24 hours.
These systems usually work together to support sleep at night and wakefulness during the day.
When their timing becomes misaligned, someone may feel tired but struggle to fall asleep at the desired time.
However, insomnia can also occur when sleep pressure and circadian timing appear relatively normal.
The Brain's Sleep and Wake Systems
Sleep and wakefulness are regulated by networks of brain cells that promote either alertness or sleep.
Wake-promoting systems use chemical messengers, including orexin, histamine and noradrenaline, to help maintain consciousness and attention.
Other brain networks help initiate and maintain sleep.
Normally, the balance between these systems changes as someone becomes sleepy.
In insomnia, wake-promoting activity may remain elevated or sleep-promoting processes may be less effective.
This can create the frustrating experience of feeling exhausted while remaining unable to fall asleep.
Hyperarousal and Insomnia
One explanation for some forms of insomnia is hyperarousal, meaning a heightened state of physical, mental or physiological alertness.
This can involve increased cognitive activity, heightened awareness of bodily sensations or changes in the systems responsible for alertness.
Someone may feel tired but notice that their thoughts remain active, their body feels restless or they become unusually aware of sounds and sensations.
Hyperarousal can also contribute to waking during the night and finding it difficult to return to sleep.
It is one recognised mechanism associated with insomnia, but it does not explain every case.
Survival Mode and Sleep
The body's stress response helps us remain alert and respond to potential threats.
When the brain perceives danger, the sympathetic nervous system and other stress-response pathways can increase alertness, heart rate and physiological readiness.
This is sometimes described as fight or flight or survival mode.
These responses are useful when immediate action is needed, but heightened alertness can also interfere with the transition into sleep.
For some people, prolonged stress or repeated experiences of feeling unsafe may contribute to a pattern in which the body remains alert even when they consciously want to rest.
The relationship can also work in both directions. Difficulty sleeping may increase frustration, worry or awareness of being awake, which can make sleep feel increasingly elusive.
This does not mean that all insomnia is caused by stress, anxiety or unresolved emotions. Sleep difficulties can arise through many different biological and environmental processes.
Sleep Fragmentation
Sleep naturally involves brief awakenings and transitions between different sleep stages.
Most of these are short and may not be remembered.
In insomnia, awakenings may become more frequent, prolonged or difficult to recover from.
Some people find that once they become fully awake, their thoughts and awareness increase, making it difficult to return to sleep.
Sleep fragmentation can also occur because of pain, breathing disturbances, hormonal changes or other physiological factors.
Insomnia and Chronic Illness
Insomnia frequently overlaps with other chronic symptoms.
Pain can interrupt sleep, while dizziness, digestive discomfort, temperature fluctuations or palpitations may make falling asleep or staying asleep more difficult.
Some people experience changes in sleep timing or alertness alongside autonomic dysfunction or other chronic conditions.
The relationship can also be reciprocal: disrupted sleep may influence pain sensitivity, fatigue, concentration and emotional regulation.
This means insomnia may be both an independent symptom and part of a wider pattern of chronic illness.
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Being exhausted doesn't guarantee being able to sleep.
Someone can feel physically and mentally drained while remaining unusually alert or unable to fall asleep.
Insomnia isn't always difficulty falling asleep.
Some people fall asleep quickly but wake repeatedly or much earlier than intended.
Insomnia and non-restorative sleep are different.
Insomnia involves difficulty initiating or maintaining sleep. Non-restorative sleep describes waking without feeling refreshed, even when sleep duration appears adequate. The two can overlap.
Waking during the night is normal.
Brief awakenings occur naturally between sleep stages. They become more significant when they are prolonged, frequent or associated with daytime difficulties.
Sleep difficulties can fluctuate.
Someone may experience several nights of relatively normal sleep followed by periods of significant insomnia.
Insomnia can occur without anxiety.
Although stress and heightened alertness can contribute, insomnia also occurs alongside physical illnesses, hormonal changes, medications and sleep disorders.
Sleep patterns can change over time.
Someone who previously struggled to fall asleep may later experience early waking or repeated awakenings instead.
Insomnia doesn't always mean sleeping very little.
Some people with insomnia obtain a reasonable amount of sleep overall but experience significant difficulty with its timing, continuity or the process of falling asleep.
Cortisol and the Sleep–Wake Cycle
Cortisol is a hormone produced by the adrenal glands. Although commonly called the stress hormone, it also plays an important role in regulating energy, alertness and the body's natural sleep–wake cycle.
Cortisol normally follows a daily rhythm. Levels tend to be lowest during the early part of the night, begin rising towards morning and increase more sharply around waking. This helps prepare the body for the day ahead.
The release of cortisol is regulated by the hypothalamic–pituitary–adrenal (HPA) axis, a communication system connecting the brain and adrenal glands.
Stress can activate this system, increasing cortisol production and promoting alertness.
Research has found that some people with insomnia experience changes in cortisol activity, including elevated evening or nighttime levels. This may contribute to difficulties falling asleep or maintaining sleep.
However, the relationship is complex. Not everyone with insomnia has elevated cortisol, and cortisol levels alone cannot explain why someone struggles to sleep.
Sleep disruption can also influence the body's cortisol rhythm, meaning the relationship can work in both directions.
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Insomnia can take several forms, and the experience may change considerably between individuals.
The tired but wired feeling: Experiencing intense exhaustion while the mind or body remains unusually alert.
The endless settling: Lying in bed feeling sleepy but finding that sleep never quite arrives.
The racing mind: Experiencing persistent thoughts, mental activity or heightened awareness when trying to fall asleep.
The sudden awakening: Waking abruptly during the night, sometimes feeling unusually alert or physically activated.
The early morning waking: Becoming fully awake in the early hours, long before intending to get up.
The fragmented night: Falling asleep repeatedly but waking so often that the night feels broken into short periods.
The unpredictable sleep: Sleeping relatively normally on some nights but struggling significantly on others.
The sleep awareness: Becoming increasingly conscious of being awake, the passage of time or the effort involved in trying to sleep.
The physical restlessness: Feeling unable to settle comfortably, even when mentally ready to sleep.
For some people, insomnia is primarily a difficulty with falling asleep. For others, the greatest challenge is maintaining sleep or returning to sleep after waking.
The experience can be particularly confusing when someone feels profoundly exhausted yet remains unable to sleep.
Some people notice that their sleep becomes more disrupted during periods of illness or increased symptoms, while others experience insomnia without an obvious pattern.
Insomnia can also overlap with non-restorative sleep, fatigue, cognitive dysfunction and other chronic symptoms, making it difficult to distinguish the effects of poor sleep from the wider experience of illness.
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Insomnia can be associated with stress, sleep disorders, chronic pain, hormonal changes, medications and other physical or mental health conditions.
Persistent, worsening or unexplained sleep difficulties may warrant medical assessment, particularly when they significantly affect daytime functioning or quality of life.
Symptoms such as loud snoring, breathing interruptions during sleep, significant daytime sleepiness or unusual movements during sleep may indicate another sleep disorder requiring investigation.
Severe sleepiness that affects safety, particularly while driving or operating machinery, also requires medical attention.
