Unless you have medically diagnosed sleep disorders, this is a product of your sleep schedule slowly shifting.
The simple solution is to go to sleep half an hour or an hour earlier every night until it's fixed. If you find you can't do it, do something exhaustive like exercise a few hours before.
I personally get 6-7 hours of sleep a night. I've never fallen asleep in class, though I've come close a few times. Just show her you're paying attention and you want to learn. She will be willing to offer you some catch-up then.
