Waking up with knotty hair is usually down to friction. Standard cotton can be...

https://www.bookmarkpage.win/stop-waking-up-to-frizz-standard-cotton-pillowcases-create-friction-that-snaps

Waking up with knotty hair is usually down to friction. Standard cotton can be abrasive, while silk helps strands glide as you sleep. If you aren't ready to switch, try a loose, high bun with a soft scrunchie