Restless Legs Syndrome
Multiple arousals during sleep, excessive daytime drowsiness, aching muscles upon awakening and crawling or restless sensations in the legs. This condition is often mistaken for insomnia

Sleep Apnea
Periods of interrupted breathing, as frequently as several hundred times during sleep. Causes of apnea include a blockage of the upper airway and diseases of the central nervous system. Apnea victims may experience excessive daytime sleepiness, high blood pressure, rapid weight gain, morning headaches, personality changes, impotence, signs of heart failure or enlargement and heavy snoring. They may also have sleep attacks during the day, similar to those associated with narcolepsy.

Narcolepsy
Sudden and uncontrollable attacks of excessive sleepiness during the day. This disorder causes an individual to sleep at inappropriate times such as while driving, eating or in meetings. Common complaints include frequent, vivid nightmares or hallucinations upon falling asleep, sudden muscular weakness when angry, surprised or amused and momentary paralysis upon wakening.

Parasomnia
Somnambulism (sleep-walking), nightmares and night terrors.

Other disorders
Seizures, bruxism (grinding of the teeth) and other conditions that cause improper sleep patterns.