Can't Stay Awake

So the past week I've been pulling a few all nighters to get essays, projects, studying done. I'm use to this as it's very typical of the end of semester but this time it's a little different. Usually I bounce back after a good 8 hour sleep but not this time. I came home from work yesterday at 3pm and have been lying in bed sleeping on and off. The most I'm awake is probably 10 minutes. Even as I type this I'm falling asleep. Am I just over tired or something else?