Cat has hair loss

Okay so I have this 5 year old cat named Tigger and he has like total hair loss probable about half way down his stomach area and on the inside and part of outside of his back legs. He is starting to lose hair in his arm pit area too. I don't know whats wrong with him. We thinks it's because he's a pretty nervous cat. It's been going on for quiet a while now but he seems to act just fine. 

These conditions are often hormone related and called "Feline endocrine alopecia."  The symptoms include thinning or balding of the coat on insides of the back legs, lower abdomen, and genital area. Distribution is symmetrical. It occurs most often in neutered males and spayed females.  You should take your cat to a vet and have him checked.  It's possible he can get simple medication to control it.