Hi, I'd like to help you with your question.
Bipolar cannot be caused by directly by stress itself. Stress is thought to trigger it, but there are many other factors that have to be in place to help a person develop Bipolar. The actual cause of Bipolar is unknown, but it is thought that genetic, biological and environmental factors all impact Bipolar disorder.
For the most part, scientists think it is a malfunction of neurotransmitters in the brain that causes chemicals to send the wrong messages and Bipolar is developed. This is why medication is needed in most cases with Bipolar disorder and traditional therapy, while still very helpful, cannot be used alone.
I hope this has helped you,Kate