For me, generally, under-stimulation (routine, rules, effortlessness, predictability) causes mild depression. Then I try to find excitement by taking increasingly bigger risks. This causes accidents/mistakes, some alarm or friction and resistance and I become increasingly manic by way of a positive feedback loop. Rising anxiety causes me to ignore more and more of my surroundings while all energy is used to keep me from failing. Options to succeed become fewer and I am forced to take even bigger risks, since those are the only options still open to maintain in control. The importance of each option grows with fewer options left. The importance of me grows. Suspicion rises with every attempt to stop me or reason with me and by my own importance. I enter a mixed state, where new options have to be added quickly. Finally, the risks and mistakes reach a point where there are no options left and I enter the post-mania stage, period of pure ecstasy with no desires, hallucinations, some more mixed and finally severe depression. I re-evaluate my options. If I see only one, I might enter a state of mania again, depending on the risk involved. As I see more and more options the depression slowly lifts.

Something like that. Maybe. Sometimes.

So, yes, it starts with (mild) depression and ends with depression (severe). Sometimes some period of stability after a cycle, sometimes not, sometimes it's just smooth, mild cycles.