I recently missed 2 doses of my Effexor and became severly dizzy, irritable, very sick to my stomach and extreamly tired. It was by far the absolute worst I have EVER felt missing a drug of any kind. I switched to Effexor about a year ago from Prozac. I NEVER EVER felt this terrible if I missed a few doses of Prozac. Why are the side effects of missing a dose sooooo severe?