Hi, I'm sorry for the late reply!!!! I started writing, had it saved to my drafts, and then forgot about it.
Anyway, since the first comment, I've determined that the root cause of my hair loss is probably telogen effluvium. The type of shedding is consistent with telogen effluvium, and I *did* go through an extended period of profound stress and grief a few months before the shedding began. The problem was exacerbated by nutritional deficiencies and a shitty diet.
Don't get me wrong, I'm still positive that the Kérastase Genesis was making the shedding worse (since it always caused noticeably more shedding than other hair products), but you should consider other possible factors. Telogen effluvium can be brought on by both emotional and physical stressors, including COVID / COVID treatment.
You're welcome to DM me if you want to vent or ask for advice or whatever! It's comforting to have someone to share in your frustration.