From an NY Times article...
Over the next several days they came in handy, especially at night, when I would wake up feeling dizzy, almost seasick, disoriented and in a heavy sweat, the pillow soaked. One night, awake and not eager to go back to lying restlessly in bed, I went online, typed in “Effexor withdrawal” and found bulletin boards full of pained, plaintive and sometimes angry posters who had quit taking their medication and were suffering a broad but surprisingly consistent range of symptoms: dry mouth, muscle twitching, sleeplessness, fatigue, dizziness, stomach cramps, nightmares, blurred vision, tinnitus, anxiety and, weirdest of all, what were referred to as “brain zaps” or “brain shivers.” While there were those who went off with few or no symptoms at all, others reported taking months to feel physically readjusted. In the face of those symptoms, many despaired, gave up and returned to the drugs.
By the end of the second week, I felt confident that I could continue on 75 milligrams a day. But then my symptoms became more physical: the chills at night and the cold sweats continued. I felt tingling in my shoulders and hands, spasms in my legs. These came and went, seemingly with no reason. And then one night as I lay back to go to sleep, I felt a quick spasm in my head as if an electrical current had suddenly been sent through a circuit somewhere inside my brain. Two more followed in quick succession. With each came a wave of nausea. I sat up. They seemed to disappear. They returned. I realized these were the brain zaps, and over the next few weeks they would come, with no distinguishable pattern, several times a day.
None of these symptoms would come as news to most researchers. In 1996, nearly a decade after the introduction of Prozac, its manufacturer,
http://www.nytimes.com/2007/05/06/magazine/06antidepressant-t.html