Hair loss that occurs suddenly and dramatically can usually be traced back to a stressor that occured 6-8 weeks prior to beginning of hair loss.
This type of hair loss is called Telogen Effluvium (note - this is different than autoimmune hair loss, hereditary hair loss, and male/female pattern hair loss).
Estrogen Dominance and Hypothyroidism
Hypothyroidism (low thyroid function) affects women 7 times more frequently than men! What gives? The epidemic of estrogen dominance among women is at least partly to blame.