I've been loosing mine for years. But I do know my Graves disease also helps throw it out.
I've been using MD hair lose support for about 2 months and I do seem to be loosing less. And my hairs dresser commented she can see new route. I'm happy.

Hypothyroidism is what caused me to lose so much hair !
Haven’t personally heard of Fibro causing it as of yet . 💜

I don't wash my hair, just my scalp. The shampoo trickles through my hair when I rinse. Since I have been doing this I have less hair loss

I have thick hair but yes I have a lot of hair loss.
And when I wash my hair it seems like gobs come out.
I use a drain catcher in the tub.
It is a crazy amount that I retrieve from it and loose from my head wile shampooing and conditioning and running my fingers through. Also my temples have been very thin since teens.
Early 20s My hair looked rat chewed it was so bad at one time. Now my hair is very nice but loose a lot.
No meds.

My hair is falling out like crazy. It's getting thinner as well. It's really bad and I do blame the Fibromyalgia for it. Iam older and have sisters with beautiful hair that is not falling out. Don't go crazy over it because it seems to make it worse.
Buy a good wig if it gets too bad.