What are some reasons I might be losing my hair?

I am very scared. I always have had thin hair but I never had any noticeable hair loss. Until lately. I have found hair on my pillow in the morning. There is always hair in the drain after I shampoo and there is hair in the brush after I brush my hair. Everyone is telling me it is my imagination and that they check their brushes and have hair in their brushes too but I know it's not the same. What could be causing this hair loss? As I said, I do have thin, fine hair but I've never noticed hair loss to this degree. I am 5'4, 112 lbs. I eat well. I smoke cigarettes but I doubt that that is at the root of my problem. I am really hoping to get to the bottom of this.

Tags:woman age 35-44 5 ft 4 in to 5 ft 7 in 110-129 lbs balding hair loss