Fighting off something

I did get up Wed morning and got a very good work out in.  I also tried to switch up my diet somewhat and eating turkey for breakfast and not letting my body know what to expect.  The problem came about noon, I had one of the worst headaches I have had in years and not sure why.  My back felt like it needed to be popped and my neck felt out of place. I went home after work and fell asleep for a little over an hour which I never do and still fought the headache until early evening when it finally broke. I turned off the alarm for Thursday and am going to pass on the gym and see if I can get my body back in order this week.  It's very frustrating but I know it won't last to long.