I took Effexor for 5 days and had to go off. My heart was poundin...

I took Effexor for 5 days and had to go off. My heart was pounding so hard by the 5th day, I thought I was having a heart attack. About the third day, I felt great, but I noticed people were looking at me funny and I realized I was acting a little hyper. By the fifth day, I couldn't sleep or even lie down because my heart was pounding so hard, it made me short of breath. I went back on Zoloft, which had lost it's effectiveness, but anything was better than the Effexor!