Sleep

"It may seem obvious but you could be getting too little sleep."

https://www.webmd.com/sleep-disorders/ss/slideshow-fatigue-causes-and-remedies?ecd=wnl_gdh_072425&ctr=wnl-gdh-072425_supportBottom_title_2&mb=Bw69jj4V%403Xd0vWN4nAvZhsBxqZqfebCTdGTM0BbxsM%3d