Constant friction from cotton pillowcases is a quiet cause of overnight...
https://www.bookmark-jungle.win/waking-up-with-knotty-hair-is-usually-down-to-friction-cotton-pillowcases-can
Constant friction from cotton pillowcases is a quiet cause of overnight breakage. While switching to silk helps, styling your hair into a loose, low plait before bed is the most effective way to minimise tangles