First I would email him ASAP. Briefly mention what you want to talk about, but that you would like to discuss this further in person. Also, professors usually put office hours when they're supposed to be in their office (but things come up, so they can't always be there), but generally, they're in their office a lot more than just the times they say they will be. You could always try to stop by his office at another time.

Also, i would definitely start seeing a counselor on campus. My last school had a psychological disabilities office also, that was able to give me accommodations for my classes (I was given occasional extra absences (1-2) and allowed to turn in some assignments a little late (1-2 assignments).) My experience has been when the professor sees that you're working on this and up front about it, they're more willing to do everything they can and be more lenient with you.

Good luck! Take care! Let us know how it goes.