Part of the Bipolar illness is that from a mania you move to a depression cycle and the first think you feel guilty about is how you misbehaved and were not that "perfect" person that you once envisioned yourself to be. Guilt is part of the illness - if you don't have guilt, I don't think you are truly bipolar. The problem is that we waste so much time on past blunders and mania mistakes that we forget we can forgive ourselves and actually admit that we are human too!
I know because I continually plunge into even deeper depression when I pick up that guilt trip that abases me even further. My brother once said that guilt is a useless emotion. It's true. So what, we made some huge blunders - but I don't think that bipolar people normally use their illness as an excuse, however, sometimes, we should admit to ourselves that we have a mental disorder and should administer some slack in our self judgment.
I have asked for forgiveness for bipolar blips and sometimes I have been forgiven (and forgotten), and other times people do not want to even speak to me (even relatives). I forgive them and when you get right down to it, that's all that's important along with forgiving ourselves.