Sleep is many brain states
Sleep is not one steady switched-off condition but a sequence of distinct brain states that come and go through the night. Treating it as a single thing that simply happens hides how much can go wrong inside it.
Performance
A neurologist uses clinical cases to explain parasomnias, insomnia, narcolepsy, dreams, epilepsy, and the brain’s unstable boundary between sleep and waking.
Bad sleep has serious costs
A person can survive longer without food than without sleep, and poor or insufficient sleep can have very serious consequences for physical and mental health. Yet modern society has long treated sleep as a necessary evil that takes care of itself.
Sleep problems need many specialists
Because sleep is shaped by both biological and psychological factors, sleep medicine often requires a multidisciplinary approach. A single specialty looking from one angle is likely to miss part of the cause.
Half-asleep brains act without awareness
Parts of the brain can wake while others stay asleep, and that disconnect lets a person walk, eat, or even drive with no awareness or memory of it. The author suggests the reverse may also happen, with parts of the brain asleep in someone who seems awake.
Sleepwalking runs in families
Sleepwalking and the related night-time behaviours appear to run very strongly in families, according to the author. This points to an inherited tendency rather than stress or character alone.
The airway is a floppy tube
The throat stays open only because many muscles hold it firm, so when those muscles relax in sleep it can collapse and block breathing. The author raises the possibility that this repeated blockage may contribute to conditions like dementia, while presenting it as a possibility rather than a settled finding.
Sleep problems can signal later disease
Some strange sleep behaviours are not just night-time nuisances but early warning signs of brain disease years away. A reviewer notes that one such disorder is described as a precursor to Parkinson's disease.
Sleep disorders can rewrite behaviour
Disrupted sleep can produce behaviour a person would never choose awake, such as frightening hallucinations, uncontrolled kicking, binge eating, aggression, or uncharacteristic sexual behaviour. A brain disorder of sleep can look from the outside like a change of personality.
Sleepiness can strike at random
In some disorders the urge to sleep becomes irresistible in inappropriate circumstances and places, even triggered by a strong emotion like laughter. The problem is not too little sleep at night but no control over when sleep arrives.
A body clock can drift daily
When the internal clock fails to lock onto the 24-hour day, sleep time shifts a little later each day and keeps cycling around the clock. The person's days and nights stop lining up with everyone else's.