Definition of Sleep disorders:

Sleep disorders involve any difficulties related to sleeping, including difficulty falling or staying asleep, falling asleep at inappropriate times, excessive total sleep time, or abnormal behaviors associated with sleep.

Causes, incidence, and risk factors:

More than 100 different disorders of sleeping and waking have been identified. They can be grouped in four main categories:

• Problems with falling and staying asleep (insomnia)
• Problems with staying awake (excessive daytime sleepiness)
• Problems with sticking to a regular sleep schedule (sleep rhythm problem)
• Unusual behavoirs during sleep (sleep-disruptive behaviors)

PROBLEMS WITH FALLING AND STAYING ASLEEP

Insomnia includes any combination of difficulty with falling asleep, staying asleep, intermittent wakefulness and early-morning awakening. Episodes may come and go (be transient), last as long as 2 to 3 weeks (be short-term), or be long-lasting (chronic).

Common factors associated with insomnia include:

• Physical illness
• Depression
• Anxiety or stress
• Poor sleeping environment such as excessive noise or light
• Caffeine
• Alcohol or other drugs
• Use of certain medications
• Heavy smoking
• Physical discomfort
• Daytime napping
• Counterproductive sleep habits:
  • Early bedtimes
  • Excessive time spent awake in bed

Disorders include:

• Psychophysiological insomnia: a condition in which stress caused by the insomnia makes it even harder to fall asleep
• Delayed sleep phase syndrome: your internal clock is constantly out of synch with the "accepted" day/night phases; for example, patients feel best if they can sleep from 4 AM to noon
• Hypnotic-dependent sleep disorder: insomnia that occurs when you stop or become tolerant to certain types of sleep medications
• Stimulant-dependent sleep disorder: insomnia that occurs when you stop or become dependent on certain types of stimulants

PROBLEMS WITH STAYING AWAKE

Disorders of excessive sleepiness are called hypersomnias. These include:

• Idiopathic hypersomnia (excessive sleepiness that occurs without an identifiable cause)
• Narcolepsy
• Obstructive and central sleep apnea
• Periodic limb movement disorder
• Restless leg syndrome

PROBLEMS STICKING TO A REGULAR SLEEP SCHEDULE

Problems may also occur when you do not maintain a consistent sleep and wake schedule. This occurs when traveling between times zones and with shift workers on rotating schedules, particularly nighttime workers.

Sleep disruption disorders include:

• Irregular sleep-wake syndrome
• Jet lag syndrome
• Natural short sleeper (the person sleeps fewer hours than normal but has no ill effects)
• Paradoxical insomnia (the person actually sleeps a different amount than they think they do)
• Shift work sleep disorder

SLEEP-DISRUPTIVE BEHAVIORS

Abnormal behaviors during sleep are called parasomnias and are fairly common in children. They include:

• Sleep terrors
• Sleep walking
• REM sleep-behavior disorder (a type of psychosis in which a person "acts out" dreams so violently that they may injure the person sleeping with them)