Off of just a 28mg pill? Really weird, you sure that was concerta you took, on erowid there are people who snort about 100 mg of methlyididate (the active substance), and nothing like that - loss of appetite yes, but nothing nearly like that.

http://www.erowid.org/experiences/ex...=Search&S1=114

Yeah, maybe you were allergic, or very prone to the effects. Drugs affect each person very differently.