What a sleep disorder is

1. A sleep disorder is a lasting problem with sleep that stops it doing its job for the person.

The symptoms of insomnia

1. The person lies awake for a long time unable to drop off, even though they are tired.
2. They wake in the night, or very early in the morning, and cannot get back to sleep.
3. The sleep they do get feels light and unrefreshing rather than restoring.
4. The next day brings tiredness, poor concentration and low or irritable mood, which is what turns a bad night into a real difficulty.
5. The pattern repeats over weeks, so daytime life starts to suffer.

Explaining insomnia

1. Stress and worry
   1. A mind kept busy by exams, money or grief stays alert, and an alert brain does not slide into stage 1 easily.
   2. Worrying about not sleeping then feeds the problem, so the insomnia keeps itself going.
2. A body clock out of step
   1. Shift work, travel across time zones or a wildly irregular bedtime leave the internal clock pointing one way and the day pointing another.
3. Another condition or a substance
   1. Pain, illness and low mood all disturb sleep, and so do caffeine and alcohol.

The symptoms of narcolepsy

1. The person feels overwhelmingly sleepy in the daytime, however much sleep they had the night before.
2. Sleep attacks come on suddenly and without warning, sometimes in the middle of a conversation or a meal.
3. Strong emotion such as laughter or surprise can trigger a sudden loss of muscle strength, so the person sags or collapses while still aware.
4. Night-time sleep is often broken rather than solid, so the tiredness is not simply a matter of going to bed earlier.
5. Dreamlike images can appear as the person falls asleep or wakes, blurring the line between sleeping and being awake.

Explaining narcolepsy

1. REM breaking into waking life
   1. The leading explanation is that the brain system controlling REM does not switch cleanly, so features of REM appear while the person is awake.
   2. That accounts neatly for the symptoms, since the stillness of the muscles and the dreamlike images both belong to REM.
2. A missing brain chemical
   1. People with narcolepsy tend to be short of orexin, a brain chemical that normally holds the waking state steady.
   2. Without enough of it the switch between sleeping and waking becomes unstable, which is why sleep arrives unannounced.
3. An inherited vulnerability
   1. Narcolepsy runs in families more than chance would predict, which points to genes making some people vulnerable.

Turning this into marks

1. Name the disorder and give its symptoms in your own clear words.
2. On a scenario, quote the detail that identifies the disorder rather than describing it in general.
3. The mark most often lost is listing symptoms when the question says explain, which needs a reason.