1. Your hair isn’t falling out. Your follicles are shrinking.
Your part looks wider. Your ponytail feels thinner. So you assume you are shedding more.
Usually you are not. You still have the same number of follicles. Each one is just making a finer hair than it used to.
Estrogen is what keeps a follicle growing. When estrogen drops, the growing phase gets shorter, so each hair has less time before it rests and falls out. The next cycle, that follicle makes something finer. Then finer again. Eventually it stops surfacing at all.
That is why this creeps up on you instead of happening overnight.
About half of women notice visible thinning during this stretch of life. Your hair is going through perimenopause right alongside you.