Paul Reading. ABC of Sleep Medicine (ABC Series). BMJ Books (2013)
Although napping most afternoons is clearly a normal phenomenon, in many Mediterranean cultures, for example, the propensity to fall asleep through the day if rested or unoccupied may well indicate an underlying disorder. Increased somnolence is usually different to simple tiredness or fatigue and particular care is needed in nomenclature and obtaining an accurate history. Some useful leading questions are given in Table 1.2.
Probably 5% of the population can be considered to have excessive daytime somnolence that potentially interferes with daily activities. The dangers of impaired wakefulness or alertness when engaged in tasks such as driving or operating machinery are obvious. One of the ﬁrst signs of excessive sleepiness is the presence of minor lapses or ‘microsleeps’. These last up to three seconds, during which time there is incomplete awareness or attention to events in the external world. A further consequence of reduced alertness is impaired cognitive processing, particularly in tasks requiring vigilance and short-term memory. Indeed, it is not uncommon for severe hypersomnolence to masquerade clinically as a dementing illness.
With increasing levels of daytime somnolence, subjects are prone to automatic behaviours, performing tasks on ‘auto pilot’ with no clear subsequent recollection. Typically, objects are either lost around the house or placed in inappropriate locations. A common situation in severe sleepiness is for the subject to carrying on writing or texting whilst half asleep, producing nonsense prose or unintelligible handwriting.