Why do Hydros make some people sick?

[IcePrincess]

SWIM has had some bad experiences with hydros. The first time SWIM tried hydros was in high school; SWIM took 3 pills and then passed out. The next morning SWIM felt like he had the worst hangover of his life. SWIM had a headache, everything felt like it was spinning, nausea --> this lasted for three days, which SWIM spent in bed, it felt like the flu.

Anyways, now if SWIM is in pain, SWIM is careful and takes half ona hydro, and prays that SWIM doesn't get sick and throw up. So. . . . what's the deal? Why does this happen. SWIM's friend who's female and weighs no more than 100 lbs takes hydros all the time (she just starter), takes them 2 or 3 at a time, smokes pot or also drinks, and NEVER gets sick. So why does SWIM get sick? This is really starting to piss SWIM off.