A dog will often head bob when there is a lame leg. Sometimes if there is pain they will also pant.
Be sure you have your dog checked by your vet for lyme as well as possible hypothyroid which are common causes. If all these are negative then there may be a shoulder and or back issue which is well treated with animal chiropractic.
Often a locked shoulder joint or a subluxation in the neck and or upper back can cause lameness. Using chiropractic adjustment, cold laser and some exercises will help fix this problem.
Please contact Dr Bruce at 781-337-1180 or indekchiropractic@gmail.com