You may continue to have bulked muscles (even obese people are often very muscular because they have to move around all that weight) but your lifestyle will catch up with you. I'm a nutritional consultant and have seen people commit slow suicide with their diets and sedentary lifestyles, so don't wait too long to start eating healthier and exercising more.
The reason your muscles are hypertrophied is because you're basically doing isometrics every time you are stiff and push against that stiffness. It tears the muscles just like bodybuilding and then they compensate and try to avoid further damage by growing more fibers and developing more motor units. So you may not lose muscle tone in your legs or arms as long as you are stiff, but that doesn't do anything for cardiac health.
The Mexitil may help with some of the stiffness, but if you're not already noticing results then it may take a higher dose.