I hope people in your situation will see your post and have good advice for you.

While preparing for my PhD, I had what was then called "a nervous breakdown." It was severe depression. I didn't finish my PhD although I was so close to getting it.

Sadly, I don't have personal experience with bipolar.

There is a famous professor in a psychiatry department who has bipolar and has written about her experiences. Her name is Dr. Kate Redfield Jamison I think. Some of her amazing books are called "The Unquiet Mind" and "Night Falls Fast." Even though I don't have bipolar these books have encouraged in my life.

I wish you only the best in whatever you decide to do and sorry for not being able to be helpful to you!