Sleep Disorders: Insomnia and Narcolepsy
Sleep Disorders: Insomnia and Narcolepsy
Not everyone sleeps normally. A sleep disorder is a lasting problem with the amount, quality or timing of sleep that affects daily life. Two disorders named on the specification are insomnia and narcolepsy. They look very different — one is about not getting enough sleep, the other is about sleep intruding uncontrollably into the day — but both disrupt the normal sleep cycle you studied in the previous lesson, and both have a real impact on how a person functions when awake.
Insomnia is a sleep disorder involving difficulty falling or staying asleep, or sleep that feels unrefreshing, causing daytime tiredness and poor concentration. It can be explained by hyperarousal (the brain staying alert) or by psychological and lifestyle factors such as stress and poor sleep hygiene.
Insomnia
Insomnia is diagnosed when a person regularly struggles to fall asleep, wakes often during the night, or wakes too early and cannot get back to sleep. Crucially, this must also cause a problem in the daytime — tiredness, irritability, poor concentration or low mood — not just one bad night. A single sleepless night before an exam is not insomnia; a lasting pattern of poor sleep that damages everyday life is.
Insomnia can be short-term (acute), often triggered by a stressful event such as exams or a bereavement, or long-term (chronic), lasting for months and sometimes becoming a cycle in its own right: worrying about not sleeping makes it even harder to sleep, so the person becomes more anxious at bedtime, which raises arousal further and makes sleep even less likely. This is sometimes called a vicious cycle of sleeplessness, because each poor night feeds the anxiety that causes the next one.
One explanation is hyperarousal. Instead of the body calming down at bedtime, the heart rate stays raised and the mind stays active, as if the person is still on alert. This can be triggered by stress or anxiety and makes it physically harder to drift off, even when the person is exhausted. The body essentially behaves as though there is still a reason to stay awake and watchful, so the natural drop in alertness needed for sleep onset does not happen.
Psychological factors also matter: anxiety, depression and constant worry all make it harder to relax enough to sleep. Lifestyle factors add to this — irregular bedtimes, caffeine late in the day, and bright screens before bed all disrupt the body’s natural circadian rhythm, making the brain think it should still be awake. Shift work has a similar effect, forcing sleep at times that clash with the body’s internal clock.
Because insomnia builds up over time, its effects reach beyond just feeling tired. Concentration, memory and mood all suffer, which can affect school, work and relationships. This is why the specification treats insomnia not simply as a sleep problem but as a disorder with real consequences for daily functioning.
Narcolepsy
Narcolepsy is very different from insomnia. Rather than struggling to sleep, the person cannot control when sleep happens. Features of REM sleep — the dreaming stage — leak into waking life at the wrong moments, blurring the normally sharp boundary between being asleep and being awake.
The main symptom is excessive daytime sleepiness: an overwhelming, uncontrollable urge to sleep that can strike suddenly, even in the middle of an activity like eating or talking. This happens because the boundary between sleep and wakefulness, which is normally tightly controlled by the brain, breaks down.
Narcolepsy is a neurological disorder causing excessive daytime sleepiness and sudden intrusions of REM sleep features into wakefulness, including cataplexy, sleep paralysis and hypnagogic hallucinations. It is linked to a faulty HLA gene and low levels of orexin, a neurotransmitter that regulates wakefulness.
Cataplexy is a sudden loss of muscle control, often triggered by strong emotion such as laughter or surprise. The person stays conscious but their muscles briefly go weak, which can range from slightly drooping eyelids to collapsing to the floor.
Sleep paralysis is a temporary inability to move, speak or open the eyes fully, happening as the person falls asleep or wakes up. It occurs because the muscle paralysis that normally happens only during REM sleep continues briefly into wakefulness.
People with narcolepsy may also experience hypnagogic hallucinations — vivid, often frightening, dream-like images or sounds that intrude as the person is falling asleep, because dreaming (a REM feature) starts before full sleep has begun.
Explanations of Narcolepsy
Narcolepsy has a genetic and biological basis. It has been linked to a particular version of the HLA gene, which normally helps the immune system recognise the body’s own cells. Researchers believe this genetic link may cause the immune system to mistakenly attack the cells that produce orexin, also called hypocretin, treating them as a threat even though they are part of the body’s own brain.
Orexin is produced in the hypothalamus and normally keeps the brain stably awake, acting like a switch that stops sleep intruding at the wrong time. Most people with narcolepsy have very low levels of orexin, so the switch between sleep and wakefulness becomes unstable, allowing REM-sleep features such as cataplexy and hallucinations to intrude into waking life. Without enough orexin, the brain flips unpredictably between the two states rather than staying reliably in one or the other.
Both disorders are classed as sleep disorders and both disrupt normal daytime functioning, leaving the person tired, unfocused or at risk of accidents. Both can also be explained partly through biological mechanisms in the brain.
The key difference is direction: insomnia is a lack of sleep, caused by the brain staying too alert at bedtime, while narcolepsy is an excess of uncontrolled sleep, caused by the brain’s wake-sleep switch becoming unstable. One disorder is about sleep being too hard to reach; the other is about sleep being impossible to keep away.