excessive daytime sleepiness

Excessive daytime sleepiness is the persistent pull toward sleep at times and in situations when a person should normally be awake and alert. It is more than ordinary tiredness after a short night; it is a struggle to stay awake while reading, watching television, sitting in a meeting, or — most dangerously — driving. The hallmark is dozing off when one means to stay awake.

In sleep-disordered breathing it arises because sleep, though long enough in the clock, is repeatedly fragmented. Each apnea or hypopnea ends in a brief arousal that the sleeper rarely remembers, and dozens or hundreds of these arousals per night prevent deep, restorative sleep. The bed is occupied for eight hours, but the brain never gets a continuous, refreshing rest, so daytime drive to sleep builds up.

Beyond simple drowsiness, the consequences are real: impaired concentration and memory, low mood and irritability, reduced work performance, and a markedly higher risk of motor-vehicle and workplace accidents. Severity can be estimated with questionnaires such as the Epworth sleepiness scale or, objectively, with laboratory tests of how quickly a person falls asleep during the day.

An important caveat is that excessive daytime sleepiness is not specific to sleep apnea. Insufficient sleep, shift work, depression, certain medications, narcolepsy, and other sleep disorders all cause it, so it should prompt evaluation rather than an assumption. When it is due to sleep apnea, effective treatment such as CPAP typically restores daytime alertness, though residual sleepiness sometimes persists.