There are differences in the amount of sleep habitually
taken by individuals because individuals choose to do
this (external factors), seem to need less sleep (’short
sleepers’), or get less sleep than they want and so feel
tired in the daytime (’poor sleepers’). Studies using bedrest
and sleep deprivation have been used to investigate
if poor sleepers show systematic differences from ‘normal’
sleepers [30], but they have not reliably shown that
the sleep homeostat or rhythm of core temperature is
different. For example, the temperature rhythm and
responses to the multiple sleep latency tests following
these changed schedules were normal in poor sleepers.
Also, when short sleepers (< 6 hours per night) and
long sleepers (> 9 hours per night) were compared, both
responded in the same way with regard to the effect of
prior wake time upon the amount of SWS and the
kinetics of SWS during recovery sleep [31]. Therefore, it
has been suggested that short sleepers endure higher
sleep pressure, and that poor sleepers are not particularly
susceptible to sleep pressure.