Other known problems with NutraSweet are: Severe headaches (neurological) and amenohorrea (cessation of menstrual periods in females). I know 2 women personally who had this happen and periods returned to normal when they stopped drinking diet Coke.
I know a gal who had the same symptoms as you — starting when she took a new job where she had diet coke available and drank a lot of it. I advised her to stop and see what happened. Lo and behold, the “spells” went away. To test further, she tried diet coke again, and had even worse symptoms.