longer fasts are not all bad though, I just have no idea why people feel the need to jump in and try to do 24 hour fasts and then feel dizzy and faint. 24 hour fasts are anything but "simple". start with 12-16 hours and work from there.
I would also like to say that unless you have your nutrition dialed in and PERFECT, you may be doing yourself more harm than good with IF. Everyone should make sure they are getting optimum nutrition, especially on the micronutirient scale, if they are going to start integrating IF, otherwise you will be dragged down and stressed very easily. Are you taking any vitamins or supps at all?