I lift weights 2-3 times and have for many years. If I quit for a while, when I go back and start lifting again, I get sick(achy in shoulders and neck area, cold chills and feverish). I recently had to stop lifting for a minor procedure that I had. Basically didn't lift for a month and when I lifted last night, here comes the sickness. Extremely tense and sore through my neck and traps and I have been running a slight fever. What causes this and is there any way to prevent it?