Most sleep disorders are in the regular medical diagnostic list. Honestly not sure which sleep disorder is listed in the dsm . The dsm is specific to mental health. Do you know the specific term,?

It might be a symptom. But I've not heard of it being a disorder in the dsm.

The delayed sleep phase syndrome is a medical diagnosis. Not in the dsm.

If you only sleep a small number of hours and wake up super early , that's a sleep disorder symptom. Typically it's a symptom of some other problem. It's common in dementia.

It's also normal to sleep less hours as you get older. So old people are notorious for waking up early.

It's natural to get tired when the sun goes down. And if you only need 6 hours of sleep but go to bed at 10 pm. You will wake up at 4 am.

So some other sleep related diagnosis:

There is also sleep apnea.

There is a long list of Sleep parasomnia disorders

Narcolepsy (2 types)

There are sleep problems related to all sorts of conditions like schizophrenia and bipolar. ADHD.

Sleep problems can be caused by drug and alcohol use.

As far as I know. Sleep problems are only symptoms in the dsm . No sleep disorder is listed in the dsm.