There are several special techniques for those who feel hunger for more than one day of fasting, i can post them to you if you are interested.
Sleeping is a very good idea if a fasting person feels weak. However, if fasting is regular (like 10 days fasting three times a year) with a sensible (full of vegs) diet between fasts, then very soon comes the time when in the first three days of fast you have MORE energy than usual.