I've noticed this too. I've found that my jaw muscles can get pretty sore over the course of a workday and I often get mild tension headaches. Not sure what to attribute this to... dehydration, lactic acid buildup, nic levels, toxin withdrawal, etc, but it seemed to be the worst during my first week off analogs. I think paying closer attention to other areas of your health will help (hydration, nutrition, exercise, stress management, etc).