My Doc at Pennsylvania Hospital (very prestigious Psych Institute) in 1992 told me that sometimes mood disorders burn themselves out. (I can't give you an answer on that. I wish they did.) I have heard of people who experience manic episodes with long dormant periods in-between.

This is a book which got a lot of high acclaim in the 90's which was written by a Dr. who is manic-depressive. I can't recall how often her mania occurred but she chronicles it pretty well. Another person who wrote about her illness was Patty Duke. Carrie Fisher has also talked about her BP in Psychology Today.

An Unquiet Mind: A Memoir of Moods and Madness: Kay Redfield Jamison: 9780679763307: Amazon.com: Books