Assume you are also changing your eating as well? Sure it's not withdrawal from junk?
Haven't cut anything out of my diet, just dropped about 250 calories a day from my intake.
Yes, I get it sometimes if I've had a break and then hammered a big workout. You're putting some real strain on your body/cns so it makes sense that if you're not used to it you'll suffer.
I just found it strange as i've had aches and pains plenty of times before but these last 2 post-workout days i actually felt like I was on the cusp of getting sick.
Think macca has nailed it in that i've also cut down my intake as well as doing slightly more exercise.