Well. Emotional swings like that can occur as part of a manic episode specifically. Mania just means the emotions come faster than usual, not that they’re good. Ppl w mania are actually frequently extremely angry, usually because they’re going a million miles an hour and don’t understand why everyone else won’t just keep. tf. up.

But yeah if op has always just been like that consistently without any ebb and flow over month’s / years then yes it points more towards a thought disorder. I used to have a really cool infographic from a textbook on the differential dx between borderline, bipolar, and adhd since they can all have very similar presentations or even just be comorbid in certain patients.