I had a chihuahua that was scared of storms, at first she would sit in a corner and pant and then later she hid behind the sofa and stayed there until the storm was over. She felt safe there and whenever she knew a storm was approaching she would run and hide behind it. I would say just let your dog be, in time he may find an area in the house he feels safe and stay there until the storm passes, it's better than giving your dog pills.

Digital Paint Pet Portraits
http://dogshop.50webs.com