So I'm a doctor and I work in intensive care - where CPR and intubation are common. The jumping up and down on the chest bit is really not the issue here - yes it would be painful if you were awake, but the patients that you're performing this on aren't going to be awake.

The process of surviving your cardiac arrest, however, is fucking traumatic. If you survive the initial event you are almost certainly going to end up in intensive care with a tube down got throat. If your brain isn't mush from oxygen deprivation during that period when your heart wasn't beating then you'll be regaining consciousness with that tube in you. You can't talk and you can't cough, even though that's what your body is telling you it really wants to do because there's a plastic tube in your windpipe. You can't move because that tube could come out so you have to shit in the bed. The opiate based sedation they give you to make that tube just about tolerable will give you crazy hallucinations and nightmares. Every day doctors will visit and decide whether you need any one of a dozen painful procedures involving large needles - you might need a central line in your neck, or a dialysis line in your groin, or a big tube poked through your chest wall to drain fluid or air from your thorax, or a feeding tube fed through your nose into your stomach. During this time (which could be months) you have the constant bonging of monitors and ventilators and drug pumps alarming, chatter from staff, lights being turned on and off all night. Intensive care is a kind of prolonged torture that I genuinely wouldn't wish on my worst enemy - but we inflict this misery on people because they might just get better and live another 20 years. But if we're putting people through this shit just so they can die of whatever's killing them 6 months later well that's simply wrong, and it's not surprising that when you discuss the realities of intensive care with terminally ill patients the majority will decide against.