It sounds like Telogen Effluvium to me. I completely feel for you / how stressful it is to lose a lot of hair in a short amount of time, but try to have faith - I'm sure it doesn't feel like it right now, but rapid onset is generally much better than news than having gradual loss as it suggests it's temporary...
I wish there were more stories like this...I can't thank you enough for sharing your success story!! I was diagnosed with low ferritin in Feb (came back 11) and it has given me a lot of hope over the past few months during some pretty distressing times.