Some people manage to be depressed and manic at the same time.
I'm one of those people. During a mixed state depression, I feel lost, empty, forlorn, and hopeless. These feelings are compounded by the dysphoric mania, and make me feel desperate, panicky, and threatened. Having all of these feelings intertwined is absolutely hellish, and it is during mixed states that I am the most vulnerable to the impuses to commit suicide. This isn't actually a phase of bipolar disorder, but it is often a critical component.