Sadism, the counterpart of masochism, is the enjoyment derived from inflicting pain. Although this is a popular view, this pain does not necessarily have to be physical pain. Sadism can also take the form of emotional sadism where the subject is not physically but mentally tortured. Sleep deprivation and playing with the subjects fears are both classified as sadism.
History’s most famous sadist, Marquis De Sade, is often blamed for ‘developing’ this form of perversion but today many psychologists and doctors have found sufficient prove that sadism and masochism create strong physical reactions inside the human body.