Unexpected Side Effect/Withdrawl??

I'm into the 4th day of Juice fast... so far have been pretty much symptom free except a little headachy. Woke up today with a completely unexpected symptom - a lot of shooting pains in the joints and muscles in my legs! This seems pretty strange (I'm 31 and it usually takes a lot of exercise to get sore muscles in my legs and I've never had leg pain like this before)... could this be a withdrawl symptom???