History, sleep study
Delayed sleep phase
syndrome is a type of insomnia
caused by delaying going to bed, which causes one to go to sleep later and later. Once they go to sleep, they sleep normally.
This is diagnosed by taking a careful history and possibly doing a sleep study
. Treatment is improved sleep hygiene
to get to bed at a consistent time. This resets the sleep cycle to the desired time.
Answer assisted by David Miller, Medical Student