I'm also bipolar. And yes, the depressive phase is horrible.

I don't recommend disclosing your health status to your employer. Especially given what you've said about its current situation. Just ask for a couple weeks off to deal with family matters. Given what you say about their vacation policy, I don't see the point of resigning.

I was in therapy on and off for decades, before a smart psychiatrist put me on lamictal (mood stabilizer) and modafinil (mood elevator). I have no clue whether that would work for you. Some still swear by lithium. But definitely don't get on SSRI/SNRI. They could make you seriously crazy.