If it helps - sadism and masochism are only diagnosed as disorders by the DSM-IV TR (2000) if, "The fantasies, sexual urges, or behaviors cause clinically significant distress or impairment in social, occupational, or other important areas of functioning." So, if everyone is consenting, and enjoying themselves - there is no disorder.

My caution is always to trauma survivors - don't engage in this unless you've talked to a therapist first to figure out if it's emotionally safe for you.

Take care, Slippers