I woke up with the tube in, and had some difficulty staying awake. I'd be fine, write left-handed, upside-down notes to people, nod my head, then roll my eyes up and pass out. Unfortunately, I kept forgetting to breathe when I passed out. I might have died or suffered effects of anoxia, had they not left it in.
The tube keeps you alive for those hours before you're functioning again. It's not your enemy, and it's not going to let you down. Your blood oxygen level is monitored - with an alarm - and everyone will know if you aren't getting enough oxygen, including you. The Tube Is Your Friend.
When you wake up, you will know what it is, so there is no reason to panic. In fact, it's the surest sign of great news. I knew I was done, and I was alive. I wasn't cursing the tube. It was a harbinger of good tidings.
I even played with its capabilities. When else can you take a vacation and be so lazy you don't even have to breathe?
You can't breathe against it. If you can hear the machine, you can time yourself to breathe along with it, if you like. You don't have to, though. Often, the machine is too quiet to time yourself to it anyway.
I am claustrophobic and have an intense gag reflex, and as far as I am concerned, the tube is blown all out of proportion. Why should anyone panic about it being there when they know full well beforehand that they wouldn't be alive if it hadn't been there? It doesn't hurt. It doesn't gag you.
Have someone bring a pad and writing implement, so you can communicate. You may wake up with one or both hands restrained, depending on what thrashing you may have done before awakening. Be calm, and they'll remove the restraints. Be frantic, and they won't. Discretion wins here.
Remember, the tube's a good omen. Have patience, revel in the fact that you're through the tunnel and awake.
Best wishes,