Back to manual PH failure... so what if it comes down? Apart from being scary I can't really see anyone taking major damage from a dropping top. Mechanically it would be most of the way down before falling (to the point where pulling down becomes the top dropping) and at that point it can't be more than a few inches from the body asleep in the PH bed. When it snaps shut it seems like a lot, but remember it's not going all the way to the bed- it's a lot closer to that breakover where it really starts accelerating down. I suppose if I made a habit of sleeping on my back I'd be worried about taking it in the nose, but otherwise it doesn't seem like that big of a deal.
an electrical failure causing the electric PH motor to run in the "close the top" direction while you're asleep on the PH bed... that's something you can lay awake worrying about. Imagine, even after the house battery dies and the motor stops trying to crush you, you're still not going anywhere because unlike the manual you can't move the top and whatever brought it down to climb out.