As someone who spent nine years sweeping up hair at the front desk, I know...

https://source-wiki.win/index.php/Is_sleeping_with_wet_hair_making_breakage_worse%3F_The_truth_from_behind_the_salon_desk

As someone who spent nine years sweeping up hair at the front desk, I know exactly what happens when you hit the pillow with loose hair. It is all about friction