I, personally, do think stressors of all sorts (even seemingly positive ones) are major triggers for bipolar episodes, but I believe that one would not have a bipolar episode without being genetically predisposed to the condition. I think my first episode when I was very young was sparked by a major stressor, but I have had plenty of episodes start up seemingly for no good reason. I could possibly believe that people (or at least me) are very very sensitive and can find stressors or other types of triggers in things that barely or completely don't affect those without the disorder. Something like change in seasons or hormonal issues might be an example. Or even one thing said that bothered me and I stayed up late ruminating on it.

I also think mood episodes are triggered by other mood episodes. The well-known "What goes up must go down" effect, or vice versa. This seems to also be possible with a period of stability in between. Many say that just as the "kindling effect" makes epileptics more likely to have frequent seizures, the same can make a person with bipolar have multiple episodes, but this is not always the case, I guess.

I think therapy can be very helpful in preventing bipolar episodes. My psychiatrist requires that I have therapy because he believes it represents a complete treatment. Certainly learning coping skills and have that extra support may help some people be less vulnerable to stressors/triggers.