Plan to do it with handcuffs or restraints of some sort. First, place one restraint on, then The only challenge is getting the very small garbage(sturdier) bag on, taped/elastic banded, spending a couple seconds willpowering that second restraint on behind your back.
After than , place yourself somewhere quiet, in the back of a vehicle or if your alone, your bed, smaller confines and isolation is better for covering up the big noise.
Yes, the body will still trash even after that magical 2 minutes of consciousness, but you won't be able to tear it off.
My guess, you will have 1-15 seconds of pre panic.
30 seconds of starting panic, where you still have willpower to 'try' to not remove the bag, your heart will feel heavy, your pulse will spike(the heart will beat more blood full of sweet O2 to the body to compensate for the carbon dioxide levels spiking..
Another 45 seconds of sheer panic, uncontrollable survival instinct is here, this is why we restrain ourselves. Your heart. Will feel like a brick, it will beat strong, fast and hard, so hard it feels like it's going to jump out with each pump.
Then you WILL feint, go Unconscious, it will mercifully take you as another commented. Don't eat or drink 'alot' before doing this, let the fluids and food pass through your stomach for a couple hours, you don't want the last thing you remember to be vomit in your bag(the body will be convulsing still remember). Not that I think you'd remember it, if you did it right you should be dead.
Eitherway, this method may be shocking for those who find you but you will appear normal, open casket worthy, no hideous holes, cuts, cyanosis(blue-face) from hanging, it's quicker than most( 1.5-2 min concious time, then it takes you quickly).
Rescuers like another said don't have long to resuscitate you. 1.5-2 min to Unconscious 4-6 min to clinical death (breathing and heart stops) 6-10(not 15) min to biological death (irreversible damage to brain)
20 minutes(2 concious) max from bag to biological death. That's about as long as it takes me to have a shit and be done with it.