That won't work. You can't fall asleep with your arm up, when you get to sleep, you go limp. It also takes energy to keep your arm up, that means a little bit of adrenaline. Adrenaline is a very powerful stimulant.

The theory may work for WILD though. If you leave your arm up, then let it fall, it's possible that it will trick your mind into thinking you went into SP. I do something similar to induce fast hypnosis as a party trick. However, I still think the adrenaline will keep you up.