I got a concussion when I got conked (which, tbh, kinda goes hand in hand. Getting knocked out is literally your brain bouncing off ur skull, which is very concussive, as you might imagine.) And I literally slept for like two-three days straight. During the first day or so, I was really nauseous whenever I stood, or even sat, and I had no apatite at all. rip all that hospital food that got thrown away after I didn't eat it.
As far as how disoriented I was, I was very. Did I know that about myself? hell naw. I thought I was perfectly cognizant.
When you're writing a character who is going through that, you should try to show how disoriented they are without actually having them notice. Like for example, I had a possible neck injury too, and when the doctor wanted to remove my neck brace, she asked me some questions and told me to answer without moving my head by nodding or shaking it. I nodded or shook my head every time. I couldn't remember the instruction until after I'd moved. But It didn't occur to me until later that it was because I was mentally disoriented.
When I got home, I was probably pretty out of it for at least the week. Of course, there was a lot going on too, family coming and going, etc. I Don't remember much of it, and I really wasn't aware that I was anything less than perfectly functional until much later. Just as a reference to how bad it can get, I was told I couldn't drive until a month after my release from the hospital, just in case my brain was still struggling from the concussion. So I'd hazard a guess that you can easily remain mentally impaired for that long.
One last note, the headache really wasn't super present. I can't remember if I was on pain meds in the hospital, but I sure wasn't at home. I needed 22 stitches, and obviously I got hit really hard, but there wasn't that much pain. the other sensation were a lot stronger, like the balance issues and nausea and disorientation. But most of it I really wasn't too aware of. I felt pretty out of my body, to the point where, again, I didn't even know it myself.
I hope that answered your question, let me know if not!