You are correct, this is REM Atonia

When people say that they have seen the flashing lights, it is in their mind's eye.

Do this exercise for me: Visualize a square. It is pink, with a black outline, with the image of a yellow star in it. You could "see" the square in your imagination. That's what people mean when they say that they "see" things during HH.

Pertaining to your question about the length of paralysis, everybody experiences different things, do just don't worry about that.

As for your problems with lack of length in DILDs. Your WILDs are probably more intense because you are going into them with a more aware mindset, you just have to train your awareness in your DILDs to be higher and they will last longer and feel more vivid. You do this by being aware of your surroundings and sensations that you are feeling within the dream. Ground yourself in the dream environment using all of your senses and you will find that your DILDs get a lot more vivid, clear and lengthy