Searches for auto-fellatio (sucking your own cock) and auto-erotic asphyxiation (choking yourself when jacking off) have both brought recent page views. These two topics have been covered here once each (I think).
The former is pretty common - probably more common that you might think. It takes a limber body to be able to fold over like that. Having been a dancer, I can personally attest to the pleasure of it.
If you want to be able to self-suck you'll need to take Yoga or dance classes.
But you'll have to stick with it because it takes time to limber up.
The latter, well, that's something which hides in the shadows. People don't admit to it very readily. Proponents say it makes the cock harder, thereby heightening the resultant orgasm.
Erections are a known side effect of strangulation / asphyxiation. It's the lack of oxygen that makes the cock get harder as blood rushes to organs to save them from death.
It's the same thing with cold - the cock will retract as far into the body as it can, but it might also start to get hard to provide blood to preserve the organ.
Guys know that the harder their cock is, the more intense the sensations - particularly in the glans (the head of the penis). The more sensitive the cock, the better the ejaculation will feel when we cum.
Being alone for auto-erotic asphyxiation is not a good thing. The worst that can happen is fully depicted by actor Andy Devine in
from an episode of Game Over Man on Netflix. Erotic asphyxiation is one thing if you have a partner - a spotter - with you.