bent axle shaft

My car has a bent axle shaft which caused vibrations at high speed and when braking - had the rotors replaced. What causes this and can it be repaired/bent back or should it just be replaced instead?

My car recenlty had a balance and the guy never put the lug nuts on properly and one of the front wheels came off whilst being towed to the garage - could that be the cause of the bent axle? - the other front wheel had really loose lugs too so Im lucky to be here....any help appreciated