I say Hypo, it's not uncommon for a negative intrusive thought to pop up in any mood. Intrusive thoughts are common in Bipolar.

If your not able to notice a mood shift then I would advise you to chart your moods daily, it can help point out a pattern "before" you can actually see it . This can be done on your phone , many apps are free or you can just use pen and paper. Might be of help for you.

Takes me 2 mins to chart nightly. Simple

Good Luck