I Have bipolar and i kind of feel like its influenced by both internal and external factors. Sometimes my mood changes dramatically for no apparent reason or maybe the reason is so small i don't see it.
In my experience no amount of pills, diet etc. can cure it you just have to learn to manage it the best you can and try and keeps the ups and downs from becaming too extreme- not letting them destroy you- the only thing that keeps you going is hope. Even when there is no realistic hope you have to keep a fantasy of hope that your suffering somehow has a purpose that only God knows.
Everything will be balanced out something good will happen to out weigh the bad.
Sorry this probably doesn';t make sense i'm starting to go manic- and i disagree that that is better than depression with both comes a lack of control a lack of insight and ultimatly damage to yourself and your life- all we can strive for is an ounce of stability- an island in the chaos.
Hope