Constant friction from cotton pillowcases is a quiet cause of overnight...

https://www.primary-bookmarks.win/waking-up-with-knotty-hair-usually-comes-down-to-friction-against-your

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