Personal opinion: I think there are a lot of reasons. Part of it could be depression, which definitely makes you tired. Part of it could be due to a poor diet, all that pizza and sweets is a perfect recipe for sugar rushes, crashes, and a general lack of energy to do things, deficites of certain things like iron, b-12, and other nutrients can definitely influence/cause chronic fatigue. Part of it is a lack of exercise. I think when you just sit around all day and don't "get your blood moving" as my mom refers to it, you tend to feel groggy and sleepy during the day, and then when she is actually doing something she is not used to the effort and gets tired a lot more quickly. She has a lifestyle that is full of reasons for her chronic tiredness.