Drained

For the past month I've just been drained of energy. I don't know why. It sucks. I'll be sitting in school feeling fine and then all of a sudden a powerful force of sleep overcomes me. I know it's not from my sleeping habits, since everyday I come home and go to bed at 7 or 8.  I've actually been getting the greatest sleep of my life but yet I get hit with drowsiness in the middle of the day. First, my body feels physically exhausted and all I want to do is sleep and sometimes I doze off in class; which I hate doing because it's so disrespectful, but I really can't stay awake. Now, if don't go to sleep and be disrespectful in class I become very irritable and I get annoyed at everything, so either way I'm a bitch by either sleeping in class or being irritable if I stay awake. I hate it. It's frustrating not to know why I get so tired like this too. I hope it stops.