I forgot to answer the second part of this.
Until my 30s, my moods would change every few months. The bad episodes lasted 4-6 months, but usually closer to 4. The bits in between could be weeks, months or years, and I would be absolutely fine at those times. I have asthma as well and it was a lot like that... flares with good health and maintenance therapy in between.
However, somewhere around 39/40, the pattern changed quite a bit, and I'd slip in and out of depressive episodes. Sometimes the medication cuts them off after 2-4 weeks, which is amazing when it happens. More often, I have good, normal and depressive moods and thoughts during the same day. I feel worse in the evenings, which is an atypical presentation.
The people that know about it often ask whether I'm bipolar. I can fully understand why, because I can be lively, silly, giggly, busy (in the context of being an introvert +++) and I never, ever switch off. I'm not bipolar though. I've never had a manic episode, or delusions, or behaved recklessly. I just have a silly personality!