I find exercise really good for getting rid of the excess adrenaline or agitation when I'm anxious. Now...I wouldn't recommend exercising at 4:00 am. However sometimes when I wake up early in the morning before work and can feel myself being a bit anxious or agitated, and I know I wont get back to sleep, I will get up and exercise on my elliptical machine for 45 min, and then, depending on how much time I have, I may do 40 min of yoga.