Is it normal for moles to fall off? i just had my 3rd one fall off of my leg. is it serious?

Typically : Typically moles do not fall off. It is possible that you have seborrheic keratosis, and that these fell off. It would be worth your while to get to a dermatologist in order for that physician to evaluate your condition & see if indeed that's what it is (seborrheic keratosis). Good luck!

Moles : Moles do not typically "fall off" since they are attached firmly in the skin . Perhaps they are seborrheic keratoses that are more superficial and prone to coming off. See a dermatologist to have the lesions evaluated.