The longest for me was a depressive episode, lasted for about a year or so. Long time, I know but my episodes, atleast until my teens came, tended to last quite awhile. Right now, an episode typically lasts about a month or so. Looking at it like my pdoc said though, look at the illness as something you can utilize, I know it sounds hard, but look at the things you have accomplished during an episode, this applies more to mania though, I can write like a 10 page essay in 5 minutes when manic lol, probably won't make much sense but hey it is what it is.