Hello and Welcome to Healing Well.
Effexor from what I have heard may be the toughest of all the AD's to withdraw from due to the brain shivers and the other symptoms. My guess would be your coming off the Effexor to fast but I will let the people using the drug or past users share their opinions. I just want you to know your not alone.
You have tagged on to an old post from 10/2006. May I suggest you start your own thread and also post in this thread.
https://www.healingwell.com/community/default.aspx?f=9&m=883646
Again a warm welcome to our forum which you are now a part of.