IMO, you can’t change that and you can’t control HI. They’re random. But you don’t have to be afraid.
As far I understand, what you see are not HI. They are phosphenes PLUS your imagination. What you call the “flying neon eye in the dark” (you really have found a great name!) 
is probably a phosphene that Skidzz and I have noticed in this post :
Did I just SEE my third eye?!
And about the “shadowy forms”, I noticed them too. Sometimes, phosphenes moves (they rotate or translate repetitively). Generally, when they’re static, we notice the luminous dots. But when they’re moving, the curious thing is that we first notice the dark areas between them. If these dark areas are vertical, our brain may interpret them as silhouettes and, if the dark area increases in size, as a movement towards us, which can be surprising or frightening.
So, if I understand well what you’ve seen, you should notice that they are just dots of lights, or the areas between them, and your imagination gives them a strange form they haven’t, like in a Rorschach’s test. If you notice that, you won’t be frightened. 