This isn't for everyone. I had a period when I got really into fasting (I loved the challenge), often doing 24 hour and 48 hour fasts.

However, one time I tried to go for three days, and on the third day I got suddenly extremely lightheaded while hanging out with friends, and it was a scary enough that they insisted I end the fast right there (I agreed). My enthusiasm for fasting was tempered quite a bit after that.

Maybe that wouldn't happen the next time I tried going 3+ days, but I don't want to risk it.

Also, I've noticed that driving any serious distance while even on the second day of a two day fast, or concentrating on hard programming problems, can be pretty difficult. That's the main reason I don't do it much anymore (I was in high school and had nothing better to do when I was fasting before).