I know all to well the withdrawl symptoms. It is horrible. Shakes, sweating, can't think (foggy head), crying, nausea. I have had tremendous luck with taking the medicine. Sometimes I don't have the money to get more. I call to my doctors office once because I was very scared. The nurse told me when people are getting off the medication some actually have to taper off by counting the pebbles inside the capsules and take a pebble or two less a day.
I am on Effexor and have not been the best with taking it from time to time. The withdrawl from Effexor is bad and what you are describing sounds exactly like it. I am on a much higher dose and I can't tell you how long it will last as I take mine as soon as I start feeling miserable. I know that you usually have to wean off Effexor because of the withdrawl.