I experience both too but more often than not I am triggered by stress. Any stress, good or bad, doesnt matter, stress in general can trigger an episode.

Im not talking "did your homework late" or "missed a family birthday" stress, I mean real stress, like losing a job, moving house, money issues, health issues (unrelated to mental health), death in the family etc.

When I was younger I had more severe swings that seemed to come out of nowhere, but as I have gotten older and continued therapy I am noticing that many of my mood episodes have been triggered by serious life stress but do not always pop up when I expect them to.