What would cause pain in the sides of my feet that began both at the same time. Severe. Can't stand or walk. Suddon onset.

Far too many possibilities. We don't know your age, weight, health, gender, BP, anything.

Could be anything from bad shoes to a pinched lumbar nerve to blood clots and other more serious conditions, so either answer back with a lot more information (you still won't get a diagnosis online) or go to a doctor.

Severe pain should not be ignored. Go to a doctor. If it's the same on both sides, it is probably not anything sinister, but get it checked out so it doesn't get worse. If you can't stand or walk, it needs to be checked out properly by a medical person, not someone on the internet.