Whether you are bipolar or not, you are going to have a life? Might as well work toward something that feels good when you are not feeling bad?

I would analyze your study habits. Do you do well anyway, even if you have to do things last minute? If so, I would let yourself rest a bit, read some novels (about subjects you are studying?) and lay in the sun, etc.? I learned to trust myself, that I would do what it took because it was important to me. I also learned that I did not do a whole lot of learning from my textbooks and insisting I try to read them and giving myself a hard time because I did not, etc., I figured out how I, personally, learn, and worked to my strengths (writing) instead of the generic "how to study" model.

Figure out what interests you right now; sleep, reading, getting help and support from other people, what is it? Use whatever it is to help you instead of trying to force yourself into another pattern.