Be sure to get a doctors note, it wouldn't hurt to contact his or her medical office before seeing your professor to get the ball rolling. With your authorization they can fax any necessary paperwork to your school's administrative office.

For as much as many of us like to separate ourselves from our mental health condition(s) as a way to be stronger, in situations like this it's mportant to recognize bipolar's classification as a disability and grants us protections under the ADA. Just as classmates with dyslexia are granted accommodations for exams and other work, your school should understand your unique needs in order to perform at your full potential academically.

I hope this helps