I have choked myself, and for me it is like a self-punishment for something I deem I have done wrong. It is certainly not suicidal.
As for the imagining, I get something out of the 'despair' I imagine myself having while being choked, but not such that I actually want to die. There is also something about me feeling guilty, and that guilt being relieved after being assaulted by whomever I feel is wronged by me. I am not a psychologist, however, please take what I say with a grain of salt.
I would also agree with
>>3. I am a generally angry person and it is easy to vent on myself.