I fasted for few days on many occasions. The only ill effect was that it was difficult to fall asleep and the sleep was very shallow on second and third night.

I fasted for few days on many occasions. The only ill effect was that it was difficult to fall asleep and the sleep was very shallow on second and third night. After that sleep got better. I have not noticed any dumbness. Subjectively perception even improves. This is in line with experience I read in books and articles. Sometime I use that if I need to drive a long way. I stop eating the day before that ensures that I never fall asleep behind the wheel and my attention stays sharp all the time.