Sleep inversion

Sleep inversion or sleep-wake inversion is a reversal of sleeping tendencies. Individuals experiencing sleep-wake inversion exchange diurnal habits for nocturnal habits, meaning they are active at night and sleep during the day. Sleep-wake inversion, when involuntary, can be a sign of a serious disorder.

Presentation
Individuals with the delayed sleep phase type of the disorder exhibit habitually late sleep hours and an inability to change their sleeping schedule consistently. They often show sleepiness during the desired wake period of their days. Their actual phase of sleep is normal. Once they fall asleep, they stay asleep for a normal period of time, albeit a period of time that starts and stops at an abnormally late time.

Causes
Sleep inversion may be a symptom of elevated blood ammonia levels and is often an early symptom of hepatic encephalopathy. Sleep inversion is a feature of African trypanosomiasis, after which the disease takes its common name, "African sleeping sickness"; sleep-wake cycle disturbances are the most common indication that the disease has reached the stage where infection spreads into the central nervous system.