I would get him to a neurologist ASAP. I had a Psychology professor a few semesters ago that shared her story with the class during a biological brain function lecture. She had gotten out of her car at IU to walk inside and teach a class, and as she was walking through the garage she stopped dead in her tracks. She couldn't move her legs, thought it was kind of funny but no big deal, and then the feeling subsided after about 10 seconds and she continued on. It happened again a few days later, and worried at that point she went to the doctor...5 days later she was having an 8 hour brain surgery to remove a tumor that was pushing on an area of her brain that controlled involuntary movement.
It may not be anything, but it could be something that needs taken care of right away. JWM Neurology on the north side of Indy is great, though you will probably need a refferal from his primary to go there.
Best of luck, I hope everything turns out fine for you guys!