As a judoka, I always wonder about this issue. As far as I know, someone that has lost consciousness has a risk of swallowing his own tongue and dying after few minutes.
In which position should I leave an attacker after I put him unconscious in order to avoid possibly killing him?
If you are not a trained first aider, then I strongly suggest you did a course as soon as possible. As David Liepmann said, the recovery position is generally safe. However, if you are not a trained first aider, you might miss either something or do the wrong thing or exacerbate things that will lead to the victim dying.
I am not a lawyer, nor do I play one on TV. That said, if you have rendered someone unconscious in a fight, it is your responsibility that they do not die. That is true even if they attacked you first. It means that you must contact the emergency services (112 should work in most countries) and ensure that the victim stays alive. For that, I strongly suggest being trained in first aid. Otherwise, you risk being arrested and charged with murder. Whatever, never talk to the police but talk to your lawyer as soon as possible.
If you wanted an authoritative answer, I would talk to some paramedics and lawyers.
If you choke out someone, even in a real fight, normally just stopping choking him will be enough for him to wake up. If he isn't waking up alone after 10-20 seconds, you can assume something bad happened.
That is, unless you went REALLY intense on him (that means more than 30 seconds choking him). You need about 3 seconds to choke out someone ...
And when he wakes up, he wont have much fighting in him left, so you don't need to choke him for the full 30 seconds, you'll end up hurting him.
