hair stylist weighing in... sorry for the novel.

#1, it is strongly recommended that you go to a doctor. i literally got out my textbook, and it says: "In general, anyone who has unusual, excessive shedding should see a doctor." i understand your fears and it's your decision, but just know that it's highly advised.

#2, you need to determine whether the hair is actually breaking off or falling out, because those are two very different problems. if you run your fingers through your hair, do the hairs that fall have blunt ends on both ends, or does the part that came out of your scalp still have a little "nubbin" (technical term, haha) of follicle on it? some hairs with follicles are natural, but if the majority of them have follicles, that's hair loss.

some hair loss possibilities:
alopecia areata - an autoimmune skin disease that affects people with no obvious skin disorder or serious disease. reversable.

telogen effluvium - can be caused by childbirth, shock, drug intake, fever, crash diets, birth-control pills, low protein intake. reversable.

traction alopecia - caused by pulling or twisting, like wearing tight ponytails for many years. the times that i have seen this it's been at the hairline from the hair being pulled back so tightly. how tight is your helmet?....seriously.

androgenetic alopecia is genetic hair loss which causes overall thinning. for this one, your hair follicles are actually shrinking, causing each hair to become thinner and thinner until nothing is produced. i've never done this but it's recommended that you can hold a white index card behind your hair at the scalp to see more clearly, and you should actually see the "miniaturized" (that actually IS the technical term!) hairs. do your parents or other relatives have hair loss?

i hope that's helpful!