Doctor Ellen Leibenluft describes how environmental stressors such as grief and sleep-disturbance can precipitate bipolar disorder.
There is evidence that depression and mania can both be precipitated by environmental events. In the case of depression, it’s most likely stressors - something upsetting happening, a breakup in an interpersonal relationship for example [or] grief. These kinds of stressors can cause depression in people with bipolar disorder the same way they can cause depression in people who have depression itself, so called unipolar depression. In terms of mania it seems that those stressors that cause mania are in particular those that cause people to lose sleep. Having to get up in the middle of the night to take an elderly relative to the emergency room, becoming very anxious about something and not being able to sleep. It seems that for the manic side that interfering with sleep is particularly important in terms of links between what happens in the environment and what happens with the mood cycle.