Possibly a stupid question, but are you having a menstruation cycle, and if yes, are you tracking it? I was not able to infer the likelihood by your previous responses...
I'm asking because a certain amount of being high energy before and during ovulation, and more down between ovualtion and menstruation is very common, with some people having more severe bodily symptoms (PMS) in the down phase, and there is also a supercharged version of PMS with mainly depression like symptoms, called PMDD. It's caused by a sensitivity to hormonal changes and can develop at any point in life. The monthly cycling sounds a lot like it.
(Possibly not applicable to you, then please ignore it, but maybe useful info for others).