One thing thats important here is that lately I have been experimenting with LSD + DMT. I take LSD and smoke some DMT freebase on certain periods of the acid journey. This has learned me a few things:
1. Smoking DMT on the peak of the acid journey is ok for me but the acid might be too strong so the DMT is partly wasted
2. Smoking DMT on the comedown of acid is gold: I have no anxiety and together with the acid it brings me a more dreamy DMT journey
My idea is that acid is a too strong antagonist for the 5-HT2c receptor. I remember reading a pubmed article about DMT binding to the 5-HT2a and the 5-HT2c receptor where the binding to the 5-HT2c receptor was responsible for the anxiety.
My guess is that acid binds to that receptor too, so it could either as you say 'dull' the anxiety response of your brain. Or it could be that the acid has another less anxiety producing effect on the 5-HT2c receptor and that it is too strong to let the DMT kick it from those receptors.
I also noticed that smoking DMT freebase days after taking acid still has this no-anxiety effect. I wonder if other people have noticed that too.