- DSPS causes sleep-onset insomnia. Often, DSP
individuals report that they cannot sleep until early morning. Unlike most
other insomniacs, however, they fall asleep at about the same time every night,
no matter what time they go to bed.
- Unless they have another untreated sleep disorder (such as
sleep apnea) in addition to DSPS, patients can
sleep well, and have a normal need for sleep. Therefore, they find
it very difficult to wake up in the morning if they have only slept for a few
hours. However, they sleep soundly, wake up spontaneously, and do not feel
sleepy again until their next "night," if they are allowed to follow
their own late schedule, e.g. sleeping from 4 am to noon.
- Symptoms have been present for at least a month, and usually much longer.