Slept for 20 hours by mistake

My brother is 19. He has a long history of difficulty waking up. I want to suggest he visits the doctor or has a sleep study. Last night, he slept from 9 pm to 5 pm, 20 hours. He texted me when he woke up:

“I slept for a really long time, and I’m kind of out of it. I’m trembling and I’m dissociating a bit. I feel kind of nauseous and dizzy.”

I’m talking to him now. I’m worried about him because he’s away at college. I don’t want Reddit’s medical advice—but has anyone else experienced this kind of deep sleep?