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

https://www.random-bookmarks.win/waking-up-with-messy-bedhead-is-often-caused-by-friction-standard-cotton

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