Nothing as special will happen after 72hrs of food fasting... humans can go on surprisingly long without food 8-42days and without food + water around 7 days.
It will impact there is no doubt about it, but not in such dramatic way as 'hunger induced delirium' you need much longer fast than 72hrs (talking about food fasting, not sure about dry fast). 24hrs to 72hrs food fast is quite common as part of preparations for medical procedures as colonoscopy...
