I used to be a regular Diet Coke consumer. I used to get frequent migraines. A doctor suggested that might be related. I quit drinking them and sure enough, the migraines became way less frequent. Seems like only 2% of people have this problem with aspartame [1], but some of the fear is definitely justified. Maybe that's the only neurological effect it has, but I can see why some people pick sugar or nothing.

[1] https://www.uchealth.com/articles/sweeteners-headaches-and-t...