Even then, it's not necessarily a personality disorder. Could be hormones or could be emotional dysregulation from something like ADHD, autism, etc.. Or if I'm being especially cynical, then I'd say that sometimes people who were previously on meds that made them emotionally "numb" or "flat" may suddenly (and mistakenly) feel like they're "cycling" again when they've finally regained the ability to feel emotions. It's because they're not used to feeling emotions. It's also just like people who've been heavily depressed for long periods of time and are very used to feeling horrible. Then when the depression lifts and their mood is euthymic, they suddenly think they're "manic," when in actuality, they're just feeling not depressed.