164 Chapter 20
Box 20.1Sleep structureAwakeREMNon-REMCyclesBedtime Morning**Notes:
REM=Rapid Eye Movement: the phase of sleep when most dreaming occurs
and muscle tone is at its lowest. Makes up about 25% of sleep and is
commonest towards the end of the night.
Non-REM: the deepest non-REM sleep (stages 3 and 4, shown in black) mostly
occurs in the first two cycles.
Brief awakenings are normal at all ages, and can occur from either REM or
light non-REM (shown as * in diagram).
After early infancy, falling asleep is a transition to non-REM sleep.
Sleep cycles last about 50–60 minutes in childhood, increasing to 90–100
minutes in adolescents and adults.
Total sleep declines from an average of 12 hours per day in 4-year-olds to an
average of 8 hours per day by late adolescence.of infectious diseases, so good and bad ‘sleep hygiene’ alter the risks of
sleep problems. Box 20.2 lists some of the key components of good sleep
hygiene.
Epidemiology of sleep problems
Very severe sleep disorders are rare, for example, narcolepsy affects fewer
than 1 in a thousand children and adolescents, while some degree of
obstructive sleep apnoea affects 2% of children and adolescents. Less
severe sleep problems are much commoner, for example, about a quarter
of preschool children have significant problems getting to sleep or stay-
ing asleep, while up to 15% of adolescents have an erratic or delayed
sleep–wake cycle. Sleep problems are particularly common among chil-
dren and adolescents with intellectual disability and are also linked to
physical disabilities (for example, cerebral palsy), sensory impairments (for
example, blindness), psychiatric disorders (for example, generalised anxi-
ety), and physical disorders that worsen at night (for example, asthma) or
that cause night-time discomfort (for example, itching due to eczema).