Being a sadomasochist am I mentally ill?

Yes. That would be a distinct possibility. You need to see a psychiatrist to sort it out.
Enjoying pain. In our society the idea that one can derrive pleasure for inflicting emotional and physical pain on others or receiving is not exactly what is considered the norm. What do we know that sadomasochism, hypersexuality and autism seem to be linked to injury or lesions in an area of the brain called the amydala-hippocampus (muller and others 2011) this opens the door in alleviating obsessions of s & m.
Consensual Sex Play? If U R referring 2 sadomasochism as form of sex play that people engage in *voluntarily,* w/ the consent of all parties (AKA S&M), yes, many ppl engage in it & find it pleasurable. S/M pushes the boundaries of pleasure & pain. The fact that all parties CONSENT 2 engage in this play & respect one another's wish 2 STOP AT ANYTIME is what sets S/M apart from abuse, physical assault & sexual assault. .