Dead hair!!
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Well hair is pretty much all dead cells...you can keep it hydrated but it's not living. idk what all you've done, but it's possible that it may have been so thin that the new growth of hair didn't make it inside, so eventually, the natural shedding kept on going and without new hair going in it could have just thinned weakened to the point where it fell out when you pulled. it happened to a few of mine and I got freaked out too, but then I noticed the root was really super thin so it's not like there's a chunk of hair missing from my head