Stress and other nervous issues can cause hair and nails to slow their growth. My hair got very thin and fine from the stresses of this past year. I put more effort into combing over the thinner areas now than I ever did before. It is frustrating but I've learned there is little we can do about it. Worrying and fretting only makes it worse.

As you said, hats work. Thinning hair can make for a cold head. I have a hat we call "Elmer" as in Elmer Fudd, Bugs Bunny's nemesis.

Sometimes, we just have to learn to laugh at our struggles.

My best to you.