People, who do fasting over weeks, tell me, that the first days are filled with horrible cravings, headaches and hunger. After that it is mostly smooth sailing

People, who do fasting over weeks, tell me, that the first days are filled with horrible cravings, headaches and hunger. After that it is mostly smooth sailing and they talk about having more energy despite eating almost nothing. The body uses the fat reserves and muscles for energy. When these reserves are used up, the body will shutdown different functions and at the end, die.