Sensitivity to stimuli affects me when I'm in a normal mood. But it gets worse the more psychotic I become. Or put another way, I am more likely to feel paranoid and have extreme startle responses to small sudden noises, flashes of light, and hear or see things that aren't there when my sensitivity to stimuli is more pronounced.
At those times, it becomes extremely difficult or impossible to filter out various sounds and comprehend what someone is saying. Reading becomes impossible. I then need to get away from all stimuli, such as hide in a dark room with a pillow over my head until my head stops swimming with pain.

Agitation is something I associate more with emotional and bodily behaviour - such as restless legs, inability to sit still, feeling extremely wound up that I don't know what to do with myself, intense frustration, highly impulsive behaviour and difficulty controlling aggression. This I associate with a mixed mood episode.
The stimulus overload issue above isn't always part of a mixed episode for me, but can occur when I'm feeling quite normal mood wise.