Eyes have myopia of -4.00 and -4.50 and i am 29/male/white. have had astigmatism since i was very young. am afraid of pathological myopia. is this rare?

NMS but: This is not rare but you need to have regular eye checkup since the risk for retinal detachment is higher with high myopia.

Not likely: The amount of myopia you have would be generally classified as moderate (you say you have astigmatism but your prescription as described does not show it). Pathologic changes in the eye are more typically seen with higher degrees of astigmatism than you have. To be sure, you should have a dilated examination with a careful check of your retina and the retinal periphery.