I'm sorry to hear that - and I hope you're doing fine now. I really didn't have any "bad" experience like that (mania is awesome fun ;)), of course, the downside was depression followed by years of medication. They make such a deal about it being a "bad idea to leave midway through" ... I'm glad your teacher said you should (although even then, they're really ejecting you in what must be a pretty vulnerable situation). Anyway, hope you're doing fine now.
No, they certainly shouldn't... for various reasons I did a vipassana 10 day silent retreat back in 2010, and, ended up triggering a bipolar episode[0]. No, there was no history of that in my family, it was a complete surprise.
This obviously doesn't happen to everyone doing it, but, while my blog is very much buried now, I still get yearly mails from people saying that the same thing happened to them..