What Britt said is true for me too. Even though I sometimes can only recognize it in hindsight, there is a difference for me between self injury for control/emotional release, and the blatant reckless risk taking behaviour that could... hopefully... lead to my suffering a fatal misadventure...
The former is a definite and desperate fightback against the pull of death, while the latter is the indirect, but very real, path towards it.
But sometimes, in very confused and distressed emotional states, I'm not really sure what's driving the urges and know too that staying very very still and quite literally limiting all activity and movement, is the safest and only thing to do. So far I've been lucky. A primitive survival part of me that isn't even linked, apparently, to my conscious sense of whether or not I want to keep living, does tend to kick in and more or less place me in "standby mode". I know it's kept me safe sometimes.
Having just begun to emerge from a terribly bad bout of depression, this topic is very raw and real for me right now. I have been more genuinely suicidal in recent days/weeks than I have been in a long time, and I have to say... I'm terrified. Something in me just feels different now, as though I've just survived a major cancer scare but know that I'm really only in remission with a high chance of even more devastating relapse. I cant' really explain it, but I just feel like I'm not the same anymore and maybe never will be. I hope that's just the depression talking...
Maddog