A rare chronic form of sleep disorder involving a disturbance of the circadian rhythm. Patients have a consistent one or two hour delay in the time the go to sleep as well as the time they wake up so their sleep pattern doesn't fit into the 24 hour cycle. Thus, the sleep cycle changes every day which can be very disruptive. It has most often been reported in blind people. More detailed information about the symptoms, causes, and treatments of Hypernycthemeral syndrome is available below.
Source: Wrong Diagnosis