I wouldn't worry too much if it was from a 2 story height, not cause it's not high but because it's high enough for the cat to prepare for landing thanks to their righting reflex, this reflex is what allows a cat to know which way is up and which one is down, allowing it to land on its feet. They develop this reflex at a very young age(if you hold a kitten belly up you'll notice how it "twists" because he is trying to accommodate itself for a proper landing).
Cats are capable of this thanks to their flexible vertebrae, the image below shows how a cat moves its body in order to achieve a proper landing position.
Also, it's thanks to their size and weight that they can achieve this, being so small allows them to have a very much slower terminal velocity(max speed while on free fall).
Although, if you're really concerned you can always take the cat to the vet, there's nothing wrong with being extra careful.(Injuries can be sustained, but it really depends on height, and cat's ability to successfully position itself)
From this link