sCIeNCE iZ sT00piD Y0!
First of all catagen phase takes two weeks before a hair falls out, meaning any hairs you shed a week after starting finasteride were destined to fall out a week before starting finasteride. Also, finasteride continues working more than a week after taking it, so if it was causing your hair to go into catagen phase it would have continued doing so for at least one week after you stopped taking, and since those hairs take two weeks after entering catagen phase before they fall out, then you would still have been shedding tons of hair 3 weeks after stopping finasteride.
Finasteride does cause shedding when it's working because it sheds miniaturized hairs that then grow back thicker. No doubt you experienced some shedding from this, and if you had stayed on finasteride those hairs would have grown back stronger than before. So in a way, you did f*** yourself.
First of all catagen phase takes two weeks before a hair falls out, meaning any hairs you shed a week after starting finasteride were destined to fall out a week before starting finasteride. Also, finasteride continues working more than a week after taking it, so if it was causing your hair to go into catagen phase it would have continued doing so for at least one week after you stopped taking, and since those hairs take two weeks after entering catagen phase before they fall out, then you would still have been shedding tons of hair 3 weeks after stopping finasteride.
Finasteride does cause shedding when it's working because it sheds miniaturized hairs that then grow back thicker. No doubt you experienced some shedding from this, and if you had stayed on finasteride those hairs would have grown back stronger than before. So in a way, you did f*** yourself.