Dreams and nightmares are characterised by a narrative or sequence of story-like events which are often illogical with people and places disconnected. They can be recalled immediately after waking but soon fade from memory.
The content of the dream is often something which has happened in the last 2 or 3 days but significant events for the individual which took place many years ago may be recalled and may often be the basis of repetitive dreams.
There has been much debate about whether dreams occur only in rapid eye movement (REM or dream) sleep or in non-rapid eye movement (NREM) sleep as well. It is now thought that in NREM sleep any 'dream' content is much simpler with less of a story, less motion and less emotion. In REM sleep the sequence of events can be extremely complex and emotionally charged.
Pre and post sleep dreams
Dreams usually occur during sleep but may arise either just before sleep has started or after waking. This occurs particularly in people who are deprived of sleep and with jet lag but may also happen in sleep disorders such as narcolepsy [link to narcolepsy page] in which the pre and post sleep dreams are particularly vivid. The content of this type of dream can sometimes be controlled by the subject (lucid dreams).
It is unusual for dreams to occur soon after falling asleep since the first cycle of REM sleep is usually around 90 minutes after falling asleep. They then occur at approximately 90 minute intervals during sleep and are most complex and prolonged in the later REM sleep episodes towards the end of the night.
Physical enactment of dreams
During REM sleep almost all the muscles of the body are totally relaxed so that activities in the dreams cannot be physically expressed. Occasionally however this relaxation is lost and the content of the dream is physically acted out. This is characteristic of the REM sleep behaviour disorder [link to odd behaviour page] in which dreams often have a particularly aggressive content.
Nightmares are dreams which are terrifying and lead to intense anxiety or fear when you wake up from sleep. They only occur in REM sleep. There is no detectable movement until the patient wakes up at the end of the nightmare except in some sleep disorders such as REM sleep behaviour disorder.
Nightmares usually start between the ages of 2 and 5 years and are most common between the ages of 6 and 10. They are more frequent in women in adult life. They are most pronounced towards the end of the night when REM sleep is most prolonged.
Nightmares may be related to anxiety, a previous stressful situations or a result of sleep deprivation. They can be a feature of narcolepsy, REM sleep behaviour disorder and due to drugs. Investigation such as polysomnography is only needed if one of these causes is suspected.
Usually no treatment is required for nightmares. However relaxation techniques and imagery rehearsal therapy in which the dreamer is taught to change the content of the nightmares into a form which is more pleasant, may be effective.
Causes of abnormal dreams and nightmares:
- Psychological and psychiatric disorders, e.g. anxiety, depression, schizophrenia.
- Diseases affecting the functioning of the brain such as narcolepsy, REM sleep behaviour disorder, Parkinson's disease.
- Drugs. Many drugs can increase the frequency and intensity of dreams including dopaminergic drugs, beta blockers and antidepressants.
JMS, aged 60
JMS saw his GP because he felt guilty about injuring his wife on the previous night. She woke him up having been punched four times in the head. He had no recollection of this but was aware that he had had a nightmare in which he was being attacked by several strangers. He did not recognise them but fought back. He had had similar nightmares in the past in which he had been threatened by animals such as snakes coming through the wall.
His wife went with him to the GP and told him that for three years he had been a restless sleeper at night. He had often kicked his legs or moved them as if he was bicycling and had sworn and had made other aggressive comments to people who she thought he was dreaming about. He only had recall of some unpleasant nightmares but had recognised that he was having fewer normal dreams and more of these aggressive dreams.
He was referred to his local sleep centre where he underwent polysomnography which showed that during his sleep he retained muscle activity during his REM (dream) sleep. He was told that this was a feature of the REM sleep behaviour disorder and was treated with Clonazepam each night. Within two weeks his unpleasant nightmares had disappeared and his wife commented that he was no longer swearing kicking or behaving violently during sleep.