• narcolepsy: excessive sleepiness in the day and falling asleep at inappropriate times, often if excited or distressed. Associated with MS.
• parasomnias:  including: nightmares/sleep terrors/sleep-related panic attacks/sleep walking/sleep talking/sleep paralysis
• night sweats: quite a common problem in arachniacs, possibly as a result of disturbed function of the autonomic nervous system. They can also be related to autoimmune problems. If undiagnosed, it is important that you seek medical advice as they can herald serious medical conditions such as thyroid disease. Night sweats are also frequent in menopause and may be the reason for repeated wakening.
•  bruxism: grinding the teeth at night; this is quite common and may be due to stress and/or pain.  It may cause wakenings as well as an aching jaw, toothache and headaches.
•  reflux: gastric juices are more likely to enter the oesophagus when we are lying down. This reflux may be felt as heartburn (burning sensation in the chest) or even as back pain. There may also be waterbrash (taste of acid in the mouth) and respiratory complaints, sudden onset of asthma-type wheeziness (when no history of asthma before) and/or recurrent chesty cough.

These symptoms are suggestive of reflux related problems.

• headaches: four types of headache are associated with sleep:
• morning headaches, lasting 30-90 minutes, caused by lack of oxygen in patients with sleep apnoea;
• migraine headache, cluster headache and chronic paroxysmal hemicrania.

If these headaches occur soon after waking, they may be related to REM sleep, as blood vessels in the brain dilate during this phase, whereas they constrict during NREM sleep.

The more constricted they become during NREM, the more dilated they are during REM sleep. Hence if you are sleep-deprived, you are likely to have more delta sleep, so more intense NREM sleep.  Note that "Sunday-morning" headaches might be due to caffeine withdrawal (or a hangover!)

Perpetuating factors

These develop after the insomnia has set in. They include worry about lost sleep, rising late in the morning, or sleeping in the day to "catch up". This irregularity of sleep makes it difficult to fall asleep the next night, thus sustaining the sleep problem.