It actually doesn't take much energy to maintain a choke/sleeper hold. Although its pretty obvious that he couldn't manage to get a sleeper hold going on that youkai because it would have knocked him out within a minute or so if he pinched the right spot off. I'm assuming a yokai would take longer to knock out that way maybe. Sleeper holds don't actually inhibit your breathing. They just cut the bloodflow to your brain. With humans you can only maintain consciousness for just under 30 seconds when a sleeper hold is executed on ya. Martial arts is fun like that.