Even if done in the right way, full suspension is extremely painful until you fall into unconsciousness (and it could take more than 12-20 seconds for that, even if it's sometimes rather fast).
There's the one technique where you lean forward for awhile, then back off, and you fall unconscious immediately. I saw the experiment on youtube. I'll see if I can find it again. A girl leans forward with the rope around her neck for say 10-15 seconds, doesn't feel anything painful, completely conscious, no bad sensations, but when she stands back up, she passes out immediately and hangs limp, with her full body weight pulling her down into full suspension. I think her body started jerking a little bit after that, and that's when two people came up and rescued her, just to demonstrate how you can think you're fine if you're just experimenting, but then die when you stand back up.
Anyway, could be a really good way to do it, because you go immediately unconscious without much discomfort. The only issue is whether or not you wake up when the jerking starts, but I don't think the girl remembered it at all. So even if you do wake up, you're probably pretty out of it.