I had a bad reaction to Imuran a little over a year ago. It started a week or so after I started taking it, and crept in as flu-like symptoms. It continued with hot and cold flashes, body aches, uncontrollable shaking, and a nasty headache... I wisened up and figured out it may be from the Imuran. I called my Dr and he told me to stop taking it immediately. The symptoms stopped by the next morning.
Hope that helps!