I think that it is normal to have bouts that mimic depression and it's very fortunate that these bouts are recoverable. The real problem is when these bouts ended up plateauing and interfere long-term with how things happen internally and externally.

In my case I found that there were certain life events that definitely didn't help with me digging out of my hole (death, disputes, etc), but I'd want to avoid blaming any single cause. With that said, it took me a while to speak out because a part of me didn't want to come off as an attention seeker during the worst of this all.

I don't think there is a "root" cause in the end but I do feel that certain life events influence you into falling into that horrid rut.