I have thought about this too. What may result in taking off the bag when unconscious? CO2 retention if you for some reason starts to breath very quick would be my guess.
But another reason i want to tie my hands is because of SI. @TiredHorse is a good example. SI have kicked in six times (if I remember correct) for him.
Will it happen to me? Yes, and the reason? I'm very scared of failure, and our brain do EVERYTHING to keep us alive.
How do I plan to solve this? I have tried it with good results (bag over head and very quick I restrain my hand.)
I make two loops (one for each hand) I use the same knot as you would use for hanging. A slipknot, use some oil on your rope (I use 6mm rope) A rope with low friction is best. I lay them on my legs. Pull down bag and quickly stick your hands in the loops and pull tight.
What's the downside to restraining hands? If something goes wrong you can't back out. Nothing should go wrong with a positive pressure (15/lpm with nitrogen or oxygen regulator) But your brain knows that it's no way to back out, and it might result in panic. To solve this I also are going to strap myself over my chest so I can't move.
I have most things figured out, but as a very technically knowledgeable (In my own opinion at least, I would say I have the knowledge to build something like a Sarco if I had my health) person, I can't accept the roasting bag. Yes it's durable, but very thin which makes the tube to distort the bag in a way so the tube tends to fall out in the bottom. I don't know the micron thickness of my bag, but going to look for more versions. A thicker material of course also have disadvantages. It won't inflate over your head if it's to thick, unless you lift it, and then you don't know when it's filled with gas.