I lose a lot of hair in the shower too, I think it is normal, like everyone else said.

However, make sure that when you are combing through, you are not forcing your way through tangles and pulling out "live" hairs or breaking them off. I find if I am not careful when I comb my hair in the shower, or don't use enough conditioner to detangle it, I lose a lot more hair than when I coat my hair with conditioner and comb through gently.