I just told people I have bipolar disorder if they asked. I would answer any questions they had, if they were curious.
(This was in uni)

You can tell people, but don't tell them when you're in an episode. Don't try to use their sympathy because it will run out. You should have a therapist/psychiatrist and 2-3? people (including family) who should listen to you and your concerns. You can also come here and talk about concerns and have like-minded people reply to you.

A lot of people know I have the disorder, but most of them have never seen me in the middle of an episode. It's better that way for all parties.