One day, your child is going to learn how to climb stairs safely, how to go down them safely (on his bottom at first, sitting down on the step and descending, sitting down, one step at a time), how to climb onto the couch and get back off, etc. He's going to fall quite a few times between now and when he will have mastered staying upright on two feet - and that's OK.
From a sitting position, when a toddler falls over, it's only a few inches to the floor and most of the impact is amortized by the fact that the toddler doesn't usually fall, but rather rolls over (tumbles). Even if they do fall, the impact is pretty small (small distance, little weight, no starting velocity) and the head being more or less round, it's practically designed to handle that kind of impact.
Once they get upright, they usually fall either forward, in which case they put their hands before their faces and the arms take most of the impact, or they fall backward, in which case they usually fall on their bottoms first (and the fall is cushioned by the diaper as well). Falling forward may cause a bit more crying because it's scary to see the floor coming at you all of a sudden! (And sometimes it hurts a bit).
If your 9 MO bangs his head turning around too quickly and it bothers him, he'll start turning around slower - becoming more careful. That's how we learn. If he starts to yank at power cords (fun until the TV falls to the ground) you might want to intervene before the TV falls to the ground.
Monitor your child's behavior without letting him know you're watching (e.g. drink a cup of coffee pretending to look the other way) and see if he takes any unnecessary risks. as long as he doesn't, let him explore. Keep a closer eye when he does take risks but try not to intervene unless there's a real hazard (like electricity, height, weight, etc.). Your child will use you as a secure base to explore the world. If he sees you as being confident in his capabilities, he'll become confident as well but will also become prudent not to break that trust.
Wikipedia has an excellent article on Attachment theory:
Under the headings "Behaviours" and "Tenets" there are quite a few references to studies that may interest you (and reassure you).