There are a lot of variables that need to be considered. Do you nap on your bed ? Do you nap in a different position/posture ? How long after eating do you nap vs go to sleep ? What activities do you do before a nap vs going to sleep ?

How do you wash your hair ? With your head over a sink ? Tipped back under the shower ?
Do you vigorously scrub/move your head ?

I had to learn to hold my head still while shampooing and when I towel dry my hair. I have to be even more careful when the hairstylist washes my hair. A shampoo sink presents its own issues.