My diagnosis is BP 1 but I really wonder the same. I guess my diagnosis is BP 1 because I had religious delusions, delusions of reference, delusions of grandeur and some persecutory delusions too.

Sometimes I completely believed in my delusions, other times they were milder. But I have never totally lost my touch with the reality. I also had delusions where I was getting signs from God that I should do bad things to myself and that the world was ending.

Well these times when I really become delusional are rare. I am more likely to become "just" hypomanic. That's when I barely sleep, am very active, laugh at everything, even at my own thoughts, I have wasted money, cut my hair, partied many days a week with people I didn't know (I'm shy and insecure normally). I sometimes become "a creative artist" during my hypomanias, can't sit still and talk so fast others need to tell me to talk slower. The racing thoughts keep me from sleeping. Basic symptoms of a bipolar high I guess.
One time I felt creative and thought I was a reincarnation of Vincent van Gogh. I guess that was mania then.

But really I don't know where the line is, I wish I knew. Usually when the hypomania ends I start to feel crappy and either crash into depression or become delusional. Idk if that is like mixed episode or if that is the line between hypomania and mania. I've heard people say that mania doesn't (always)feel pleasant like euphoric hypomania does, but rather very unpleasant.

Once I told my nurse about my previous hypomanic episode and she asked about my sleep and when I said I slept 0-3h every night she asked: "so you were full manic?".

I guess I've only had hypomania and moderate mania perhaps but yes I'd like to know where the line between hypomania and mania goes, what is severe enough to be considered mania (without psychotic symptoms).
Sorry I didn't really answer your question.