Because we know you've always been curious, here's a brief guide to the science and forensics of hypoxyphilia, also known as autoerotic asphyxiation.
Using the death of actor David Carradine as a starting point, The Neurocritic runs through some damn interesting information behind this potentially lethal sexual practice. For instance, I had no idea that hypoxyphilia is formally recognized as a psychiatric condition under the American Psychiatric Association's current Diagnostic and Statistical Manual of Mental Disorders. According to psychiatrist Steph J. Hucker, one of the authors referenced by The Neurocritic:
The DSM-IV (TR) criterion for diagnosing the condition in living practitioners are the same as those for sexual masochism: The behaviour that results from intense and recurring fantasies or sexual urges over at least six months must be causing significant clinical stress and/or impairment (social, occupational, other).
Hypoxyphilia has been known to medical science for nearly a hundred years, and to others perhaps since antiquity, but most of what we know about it has come from the study of cases in which a mishap has occurred and the individual has died as a result of, or during, the practice. Living practitioners tend not to present clinically or to make their behaviours widely known and hence detailed insight into the paraphilia is not widely available in the literature.
For those curious, I went ahead and dug up the DSM-IV criterion for sexual masochism. You're welcome.
Tons more great links and info at The Neurocritic. Hit the link for more details.