I often feel this way but I have always been a nite owl. So I typically feel better at night.

Lithium has a half life of roughly 24 hours give or a take a few. Maybe its wearing off ? Always that chance, doesn't always mean that your over medicated , best to let your Pdoc know. When was your last Blood tests done?, and Doxapen you couldnt pay me to take that again,, Day 3 it slung me into a hellish mixed episode.

Are you on any other Psych meds? any other meds in general? anything new?

Some people do cycle more often than others, it's honestly very rare for someone to cycle daily( Gah I can't imagine) or weekly(ack), It can happen but again its rare.. Often its found that what people may label as rapid cycling is really a mixed episode or brought on by med changes or something.

I hope you find some answers