SEVERE Lexapro side effects?

I have been taking Lexapro for a while at night before I go to bed and for some reason it causes me to wake up in the middle of the night and when I try to stand up I get SEVERE nausea, gagging and retching, but I never throw up. I'm drenched in cold sweats in under 2 minutes. It also causes anxiety in me, but only at night. My question is has anyone else had these side effects, and how can I get rid of them?