First I will take sedatives until I reach a fairly high level of sedation, then I will proceed to handcuff the left hand while sitting on the bed, after which I will put the bag and close it tightly with the scarf around the neck, then I will also handcuff the right hand behind my back, at that point I will lie down, to be more comfortable I will use two pillows, it seems like I can breathe a little better although this will not prevent the feeling of asphyxiation which I hope will last as little as possible and that I will be so sedated as not to feel panic.
Once it happened to fail but incredibly I managed to free myself with the key of the handcuffs with my hands behind my back and the bag over my head which in the meantime had loosened and therefore air was getting in, I think the mistake was not doing a double knot with the scarf or tie it loosely, by moving it will have loosened; I honestly didn't have much hope of being able to free myself, it went well.
I think hyperventilating before closing the bag is useful so that you have more time before the feeling of air hunger begins and you are therefore able to finish the process with the feeling of suffocation that will begin later.
The bag I will use is medium sized, too small is not good because the feeling of suffocation starts too soon while too large will make the whole thing take too long.
In any case, fortunately, CO2 becomes narcotic after a certain level, which means that the sensation of annoying activation given by hypercapnia should not last long before a slightly more bearable condition takes over, after which you should lose consciousness quite quickly, I have no idea how long it will all take but I would say no more than 5 minutes, maybe even less; obviously it depends on the size of the bag.
I'd like to do it tonight, for dinner I think I'll just drink a little of milk, it can't be a good feeling doing it on a full stomach.