People experiencing a sleep disorder may find themselves feeling drowsy or fatigued during the day, even though they think they've had enough sleep. Those with insomnia may have trouble falling asleep, wake up during the night and have trouble falling back to sleep, wake up too early in the morning, or have "unrefreshing" sleep. In children, lack of quality sleep can result in difficulty concentrating and hyperactivity, rather than obvious sleepiness.
People with obstructive sleep apnea may snore and may feel drowsy the next day. Those with restless legs syndrome may feel a creeping, tingling, or painful feeling in the legs (usually lower legs), and may jerk their legs repeatedly as they are trying to fall asleep. Sometimes, the leg movements can be present during sleep, leading to sleep fragmentation in a condition called "periodic limb movement disorder."
Circadian rhythm sleep disturbances may lead to symptoms of fatigue and irregular sleep cycles, and often occur in patients who naturally prefer to keep very early or late bedtimes, those who travel frequently across multiple time zones, night shift workers, and those with other sleep conditions.
Narcolepsy is an uncommon sleep disorder whose main symptom is excessive daytime sleepiness. This condition may be accompanied by cataplexy (sleep attacks) and other unusual behaviors during sleep.
People with hypersomnia may feel excessively sleepy during the day and sleep for a long time at night. Parasomnias are disorders of sleep arousal that occur as the brain transitions from stages of wakefulness to sleep. Examples include sleep walking, night terrors, and talking in one's sleep.