So, do they tie a rope loosely around your neck, or something? 'Cause I don't see how you could lose all of your strength and not be able to breathe when you're nailed by the hands and feet.
You have four (or three, if one nail through both feet/ankles) points of attachment to the superstructure of the cross. It's not arms-straight-out, tied on with ropes, step to stand on, like in the Life Of Brian.
Basically you can only try to 'stand' on the nail(s) through the feet/ankles (which may be possible, depending on where they're inserted, but isn't going to be comfortable, or hang limply from the ones through the wrists. Blood-loss notwithstanding (not necessarily fatal, in itself), you're going to have problems keeping yourself 'stood up', and eventually sag to the default hanging-by-the-arms position. This drags the shoulders out and up (you can't really replicate it by stretching out that way, because that's forced out by compression, not pulled by tension) causing all kinds of problems with the breathing in the first place. But, as already mentioned, you've also got the hunk of useless weight that is the head which (once the strength in the neck starts going, or unconsciousness from all the rest of the torment occurs) cannot be stopped from lolling down and causing problem with the upper airway. There's other things to worry about, but the likes of tetanus from a rusty nail is probably not going to be an issue, in the long run.
Nice, innit?
Anyway, I got two more for you...
Adam Cancels Party: Cannot reach Garden of Eden
Eve Cancels Party: Cannot reach Garden of Eden
Eve Has Given Birth To A Boy!
Eve Has Given Birth To A Boy!
...(you can see where this is heading)
Foolish Man cancels building on sand: Dangerous Terrain