Rapid cycling is defined as 4 or more episodes in a YEAR. That's any type of episode, mania, hypomania, depression, mixed. I technically fit that description of rapid cycling, I tend to get a couple of depressions, a couple of hypo and manic episodes a year, but they last at least 3 weeks (manic) to a couple of months (depression).

There's ultradian cycling, which is when you cycle much faster. If you're not experiencing anything "full blown" it could be Borderline Personality Disorder (BPD).