Halfway through the waking period, around early afternoon, there is a strong
propensity for sleep to occur again. This second sleep tendency is part of a 12-hour
rhythm of sleepiness, that I have termed "The Afternoon Pressure for Sleep" (APS).
Evidence for this bicircadian sleepiness, include siesta cultures, short sleep latencies in
the afternoon, a midday peak in pathological sleep attacks, and the concentration of
napping to this afternoon window. The flexible nature of the human sleep/wake cycle
allows for napping to be easily suppressed, as necessitated by social and occupational
demands, and so the APS is readily masked. [Continues.]
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy at Loughborough University.