I agree with what has been said so far by cait_sith, Dark Window, and Forveleth. About what dkrw said, I do agree that fear may be greater than the pain sometimes, but I'm not sure it's always the case. In any case, feel free to ignore the rest of my message if the other answers were satisfactory. My experience is below.
Warning, my only such attempt was a while ago so I don't remember the details and everything should be taken with a grain of salt. I'm still curious about other people's experiences as well, because I'm still a little afraid to try this method again.
Some things I did to try mitigate pain was I think having a moderately thick rope (lower pressure), using padding in the form of my clothing's collar, tightening the loop somewhat in advance, making sure the rope is high on the neck, and falling somewhat slowly. I don't remember whether I was holding onto the rope as well or not though.
I think it was "unmanageable" in the sense that, had I waited any longer, then I would either want to stop it or survival instinct would kick in. The pain itself was, I believe, not nearly as bad as I had anticipated. But since it's best to stop early, I stopped it early (the main reason I tried it in the first place was that my setup made stopping fairly easy). So yeah, it was mostly because I didn't think I would last without survival instinct kicking in or the pain becoming overwhelming. On another note, according to my notes there was quite little panic if any. Probably because of the easy way to stop. I'd need to try again to actually get an idea of the pain not clouded by unreliable memories though.
After stopping: majority of the pain was along the line of the rope, probably caused by friction as the loop tightened. Mild pain swallowing. There was redness along that line, with greater pain along the right side of the neck and lower right jaw, and more mild pain on the left side, in my case. There was some blood in the region between the front-right side of the neck and the lower right jaw, with that area producing a large portion of the pain. Turning my head upward, or touching, increased the pain.
After sleeping: touching areas with redness and blood produced pain, but it was nothing compared to the spot that seemed to bruise during the process. The pain from other places decreased very noticeably after sleeping, however the pain due to the bruise seemed to not change much, if at all. The bruise was in the form of a slightly bulging out section, but the skin tone appeared to be the same as the surrounding skin. Touching the places with redness and blood produced pain, but it was very mild in comparison to the pain produced from touching the bruised area.
In conclusion, I might try it again. Or maybe partial suspension if I can find a way to stop myself from releasing the pressure, by standing up for example, during convulsions or automatic movement after passing out.