I had taken lexapro several times in my life with great success. I tried it three years ago at the time my severe AF was starting. I could not take it. I started shaking and it didn't feel good. I have heard similar symptoms from people on this forum with AF.
My guess is that you already had adrenal fatigue and the lexapro reaction was set off by already weekened adrenals. Most of us here are in various stages of healing. I have been pretty successful but am still working on the last 25% of healing.