Well, mania is suppose to effect decision making, to where a person is more reckless. For me depression makes me very irrational, though not as reckless, sometimes. So for the title question, absolutely.
Does the extreme emotional turmoil make it difficult to make decisions?
I think so. My dad passed away and life was very....cloudy for a year or so. I dated a jerk wad.
Especially if the outcome of your decision is unknown?
What if you're expecting a negative reaction to the decision? Is it even harder?
I think its hard to do things when you expect a negative reaction, like telling the truth when it may hurt.
Is it difficult to be assertive even when you know what your decision should be?
I think so. See above answer.