I've always been one for going to bed late and waking up late. I am never tired. And all of a sudden last night I was too tired to move and I fell asleep at 9. 13 hours later i was woken up by my mom and had to go somewhere and I fell asleep for another 2 hours. I've never slept 15 HOURS! I am still extremely tired right now. Also for like 4 days I haven't been hungry at all! I skip one or two meals a day. I know its not healthy but I feel like I'll throw up if I eat anymore.
Chronic depression, sleep apnea and an underactive thyroid can all cause the symptoms that you have described. I suggest you see a doctor as soon as possible.
I am not sure exactly what it could be because it could be a lot of different problems. One thing that crosses my mind is that you could also have mono, although you haven't described any other symptoms. Have you been experiencing anything else? Let me know what you think and tell us if you have any other symptoms.