A very interesting thoughts. I have heard that LD is sometimes recommended as a way to get over nightmares by doctors. There was even one temple where monks practiced LD just as you said to help them realize their own minds and feel the existence as a whole. Like the soul is still here, not matter if you sleep or not and maybe LD might be the side effect of a perfect mind-control, where you are aware of your existence every moment.

Anyway I think the negative moments work similarly to reality checks. The mind just remembers that when something goes wrong, use LD to fix it. And I believe that our minds always know that we are actually dreaming. I tried to teach myself to feel that little hidden thought somewhere deep in my brain that holds the information "This is a dream!" and it is there. Try to focus on it when you have a LD. Try to compare the state of dreaming itself to the normal waking state and you can feel something like in the back of your head, something too small to normally feel but it's there. Our mind always knows somewhere what is going on. ^^