Experiencing sleepiness at inappropriate times is not a normal condition. Sleepy individuals exhibit impairment, ranging from poor functioning at home, school, or work to potentially life-threatening automobile crashes and industrial accidents. Performance deficits occur in all sleepy people, regardless of their education, occupation, or motivation to remain awake. Patients with problem sleepiness may complain of difficulty concentrating, fatigue, and emotional lability. Problem sleepiness occurs when the quantity of sleep is inadequate due to primary sleep disorders, other medical conditions, or lifestyle factors.

Causes of problem sleepiness

For all people, sleepiness is physiologically regulated by two primary processes:

1. The body's circadian rhythm causes an increase in sleepiness twice during a 24- hour period (in general, between midnight and 7 a.m. and in the mid-afternoon between 1 p.m. and 4 p.m.) and

2. The physiological need for sleep, which is increased by sleep loss and sleep disruption

The need for sleep and the circadian rhythm interact to determine the level of sleepiness and alertness. People with disturbances of either of these sleep-regulating mechanisms can exhibit problem sleepiness, with the most common causes being primary sleep disorders, other medical conditions that disrupt sleep, drugs, and lifestyle.

The effects of drugs that disrupt sleep

Prescription and over-the-counter drugs, as well as caffeine, alcohol, and nicotine, can have substantial effects on sleep and sleepiness. For example, long-acting benzodiazepines have residual sedative effects that contribute to daytime sleepiness; beta-blockers can cause difficulty falling asleep and increase the number of awakenings; and theophylline has been shown to disrupt sleep in some people even at low therapeutic doses.

Caffeine can fragment sleep. The half-life of caffeine is between three and seven hours, so even coffee consumed during the day may be an important cause of sleeplessness at night and sleepiness the next day. While alcohol shortens the time it takes to fall asleep and is often ingested by patients for this reason, it increases sleep disruption in the latter part of the night. Nicotine can disrupt sleep and reduce total sleep time. Smokers report significantly more daytime sleepiness and minor accidents than do nonsmokers, especially in younger age groups.