Have been on Lipitor for just 4 days. I've been taking just 5 mg...

Have been on Lipitor for just 4 days. I've been taking just 5 mg per day (prescribed dose in 10 mg), and already I'm feeling very irritable and depressed (also insomnia and headache). I know this isn't considered to be a "common" side effect, but it looks like I'm not the only one out there who has experienced this. It was almost like a "switch" was thrown in my brain chemistry within the first couple of hours of the first dose. I don't think I'm going to be able to continue with this (I'm even afraid to go up to 10 mg). I'm thinking of asking my doctor about Zetia. Has anyone had depression problems with Zetia?