When I was 18, I started losing massive amounts of hair follicles. The funny thing was that the hair loss was uniform throughout the entire scalp, even the permanent zone. I probably lost 50% of my fullness in one year. Then mysteriously the hair just stopped falling out. I’m 30 now and my hair hasn’t changed since then at all. What was happening?
What you’ve described is highly unusual, particularly with the hair loss being uniform and in the permanent zone. Without examining you, I can not tell what happened to you. Since it happened a dozen years ago, I would say that the loss doesn’t seem to be telogen effluvium or some other temporary loss (though I suppose that is obvious by now).
If you are not alright with your hair fullness, then I would be happy to see you and provide an opinion about what your options might be. But at this point without an exam, I would just be doing you a disservice by guessing as to what happened.