This occurs occasionally in around 50% of normal subjects and frequently in around 6%, usually in adolescents and the elderly, especially with REM sleep rebound following sleep deprivation and jet lag following east-west travel which induces sleep-onset REM sleep. There is also a familial tendency to sleep paralysis.
Table 6.9 Differential diagnosis of cataplexy.
Epilepsy, especially gelastic and atonic
Gelastic syncope Hysteria
Table 6.10 Differential diagnosis of vivid dreams in narcolepsy.
Sleep paralysis should be distinguished from the generalized fatigue on waking which is common in the chronic fatigue syndrome and depression and is due to a lack of motivation rather than true paralysis. This lasts longer than sleep paralysis and small movements, for instance of the fingers, are possible. Sleep paralysis may also be confused with atonic seizures, transient cerebrovascular attacks and psychogenic disorders.
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