I too had bad experiences with Aspartame. It replaced saccharin about 10 years ago; as a marathon runner in his 30s, I consumed gallons of diet drinks daily at that time. When I first drank soda with Aspartame, it had immediate and severe effects upon my consciousness and vision. After a few scary incidents, soda consumption and problems seemed related. I described symptoms and circumstances to my doctor. He ran tests, but never seriously listened to my concern of relating soda with the effects. He was a reasonably competent GP, but not ready to distrust, let alone blame, and FDA approved sweetener. Eventually I quit ingesting Aspartame and have not had incidents since.
Employed in the professions and a postgraduate, I conduct research occasionally and am aware of the difficulty of matching cause and effect (and the danger of doing it improperly). But there is no doubt in my mind that “tests” with my body proved that Aspartame is bad (at least for me). When I spoke about this to a non-flying, weightlifting gym friend, he volunteered for a test. After drinking one can of diet soda, his ears started ringing within minutes and he got a pulsating sensation in his brain.