I never got the chicken pox

It's true. I didn't. I can take a bath in poison ivy with no consequence. I inherited a strong immune system from my father. I haven't had the flu since I was 10. I run at least 5 times a week, and I don't mean just going out on easy little jogs. I run faster than most people race 5ks. And I don't smoke...anything. The point being, my lungs should be in good shape along with the rest of my health. So, can somebody please tell me how in the hell a tiny seedlike ball emitted from an effing flower can cause me to get so terribly sick that I end up with severe BRONCHITIS?!?!