Yeah, ALSO fatigue can be worse in the morning, even after a good night's sleep, and then better in the evening of the same day, depending on the cause (several auto-immune diseases are notorious for an extreme version of this), and NO it's NOT "because they got up and got themselves going" and it IS that most body processes are cyclical to some degree.

ETA: Thank you for the linkspam, obv. /having a word-fail week