Hi, Psilosweet
I have something in common with you, but it's not DMT. I haven't had that experience, so I might be a good "control" for the experiences you describe. Or my suggestions might be entirely useless. Whichever way you look at it.
Seeing bright colors in swirls or geometric patterns with closed eyes is an experience a lot of people have without DMT. I'm one of them. I get that when I'm falling asleep, or often when I'm meditating. It's called hypnagogic hallucinations. Very beautiful, and sometimes they come with a "lucid" benefit--you feel like you're participating in their creeation, because they go where you want them to go and do what you want them to do.
This generally happens before you fall asleep. When I'm meditating, I try to not control them and they tend to become more consistent and less squirmy.
http://en.wikipedia.org/wiki/Hypnagogia
I also have auditory experiences with them, such as music, half-sentences or phrases. Sometimes complete sentences seem very pertient to the issues I may be subconsciously working out in my dreams.
There's another wierd experience some people have when they're waking up. It's called a hypnopompic hallucination. Feelings of paralysis usually accompany this type of phenomenon.
As far as I know, there isn't a lot of conclusive research on the neurochemistry of these events, probably because they tend to be very unpredictable.
Sorry I don't have more definite answers, but I'm including a link for you to look over.
Sweet Dreams!
OneofTwo