Yeah 20 mg is a very big dose of Zyprexa (it's the maximum FDA-approved dose I think, if I remember right).

I have been on 20 mg Zyprexa before as well. And yes, it made me very sedated. The key is to find a balance of a dose that works for you yet doesn't cause too much sedation. I am on 5 mg of it now, and it doesn't make me tired, and when I take it at night, it helps me get to sleep. Meaning it doesn't cause sedation in circumstances during which I want to be awake. It only makes me sleepy right before bed, which is ideal anyway.