MMh, don't know about meditation, I think it can actually bring out the flashbacks, the feelings since you are focusing precisely on yourself and your mental processes.
As already suggested, exercise is a better option. Go running, go swimming, go to the gym, practice your favorite sport. Do something that makes you sweat. You will feel a lot happier and better and the feelings of derealisation will go away quicker.
The terrible afterglow that your trip left you with goes away with time, it might take days or weeks, but you always come back to normal, seriously, it's a fact.
I've seen this quite a few times, in life and on the nexus too, so don't worry about that.
You say you think that the DMT experience is only an alteration of brain chemistry, and considering your current situation, you don't need to think otherwise. I don't think the any psychedelic experience is something more than that either, because of a number of facts on the matter and personal experience. I think it is a psychotic experience that in the right doses and the right set and setting can be really positive, valuable and meaningful (on cancer patients for example), but definitely not a doorway to another reality, dimension or cosmic truth.
The sense of realness can actually go really far, that's true (but the same can be said about datura delusions, schizophrenic hallucinations, severe sleep paralysis monsters under your bed that nobody would accept as real). but to me it's only a display of the power of the drug and not more. Your subconscious not believing in your rational explanations might as well be just that
When having feelings of derealisation and depersonalisation the last thing that you have to do is following the nutjob path that unfortunately some psychedelic users are into.
Exercise, go out, stay grounded, give it time and you'll forget about the bad times
