Slept 18 hours straight, is it unhealthy?

I could've slept more if I didn't have to go to class.


I have been having too little sleep lately because of Uni and stress, I pulled an all-nighter the day before but ended up sleeping 18 hours yesterday and I'm still tired. I can't afford this much sleep with the work I have to complete T_T
Is this normal?
Slept 18 hours straight, is it unhealthy?
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