You're in a terrible predicament, and of course are desperate to finish your degree.

However, I would pose this question to you: are you absolutely sure that your illness has caused that particular impulsive behavior? If not (we all do impulsive things from time to time, for no discernible reason), then I wouldn't start a potential pattern of excusing such a behavior due to BP. In your shoes, I would apologize and try to convince them that I would never do such a thing again.

Regardless of the reasons, as others have said here, and for the reasons they have cited, I would not disclose. My behavior has, especially in the past, affected my work, but once the episode has run its course, or more hopefully, been stopped in its tracks due to new meds, and I'm back to baseline, I do the best I can do and apologize when necessary. If you need an excuse, insomnia is a good one, as it may describe part of what is going on while, at the same time, not disclose BP.