I also found that I was fairly severely affected by Aspartame. However, this would send me into a depressed sleep, impossible to overcome.
I gave up NutraSweet rather easily. It always gave me a disgusting aftertaste, and I’d drink it only if there was nothing else available. A few months ago I found that someone had given me a “diet” drink despite my request for the straight variety. I waited for the inevitable collapse, but none came. Therefore I assume that it is in the type of allergy that can be controlled by rotation diets or other means of avoiding frequent use.
I’m not going to experiment with caffeine. I’ve been in great shape without it for at least ten years.