There is no way to know if this is "hypo" or your friend is just feeling great and enjoying life.

Its hard to not want to apply our " Bipolar" junk on to people that could "maybe" have something to manage like we do.

Everybody blows off work sometimes, Everyone needs a "mental health day" whether its a diagnosis or not.

Since you mention your friend is a private person well then your probably going to need to just sit back and have a "wait and see " approach. Sure you can voice your concern about the lack of sleep.

Just be a friend, I would certainly advise you against sharing your concerns at this point, that could easily blow up in your face, People mostly don't wanna hear the word " Bipolar " from a Doctor let alone a "friend".