Yes, delusions do indicate a psychotic state that could even be limited to one subject, Mandrec. It just struck me as humorous that someone would ask if a genius would likely be posting on the forum.

No, grandiosity isn't what is felt in hypomania. It might be part of Bipolar I which does
have full mania exacerbations. Hypomania occurs in bipolar, type II and is noted for
more periods of strong, long-lasting depression than frequent periods of hypomania.
I don't think one loses sanity in hypomania,(that usually appears as rapidity of thought,
spending sprees, arrogance, poor judgment in purchasing, etc.), but in full flown mania which could encompass grandiosity, I would say it's very possible to have that.
Someone I've heard about in full blown mania struck out across the street in his neighborhood completely in the nude. Another one thought he was the reincarnation Napoleon or another such historically important person. The major manic episode is one that is "around the bend" in slang terms, too.