Physical trauma to the brain, including concussions can also lead to irreparable brain damage and put the victim in a persistent vegetative state. The list of things that can break your brain in horrific ways is, sadly, not a short one. That said, cerebral hypoxia (depriving the brain of oxygen) is high on the list, and one of the reasons “just choking someone until they pass out” is not any safer than pounding their skull into a wall until they stop twitching.
Now, it’s probably worth pointing out, I was talking about grade 3 concussions. Since the question was about the character loosing consciousness, and lower grade concussions stipulate no loss of consciousness. As far as I know, more mild concussions are less likely to produce that kind of brain damage, at least on the first injury, but they also won’t knock someone out.
In deference to you; there are a lot of shared symptoms between cerebral hypoxia and concussions. There are differences, these are different medical conditions, with distinct causes and long term consequences. I honestly don’t know how much can (or should) be read into the overlap.
As always, I’m not a medical professional, though identifying concussions was covered in Scouts. Also, in fairness to you, a lot of the symptoms I think of for concussions are shared with cerebral hypoxia. The diagnostic training from first aid would distinguish them, but when I think of a concussion, the symptoms that come to mind are ones that occur with both (IE headaches, confusion, impaired cognitive function, impaired fine motor function.)