@awnlee jawkingIn 2005 at age 39 I suffered a TBI (Traumatic Brain Injury) aka "Knocked Out" by an IED (Improvised Explosive Device).
It was "Zero-Dark-Thirty" the vehicle commander, the driver, and myself, all spotted what we thought was a tripwire, nearly simultaneously; that is only relevant to the topic because we were thus alert to the following events.
I was looking down at the driver and saw a "fireball" similar to scenes in a sci-fi movie "rolling down the passageway of a spaceship" that was the blast and fire collapsing the heatshield between the engine compartment and crew compartment.
I felt like I was being electrocuted (I later discovered at least part of that was probably the sensation of several of my bones breaking, according to the doctor who treated me; I had never previously broken a bone, nor since) I felt enveloped by fire (it was a flash-fire; fortunately I was wearing fire resistant uniform, gloves, and a silk face covering). I felt a sharp, swift blow to my face, specifically the buttstock of an M240B machine-gun striking the ESS goggles protecting my face.
According to several doctors the impact with my head was concurrent with the blastwave/shockwave that "knocked out" the other three soldiers in the same vehicle. I don't recall feeling the blastwave in That Particular incident (but I did in others).
When I (we) woke up an indeterminate amount of time later (estimated at 10 to 15 minutes) {we were all unconscious/senseless and "slowly" began recovering...
My first thought was utter amazement at being alive, as I expected to have died. My thinking was fuzzy. My vision was extremely blurry; at first everything was Black; then it was shades of black and very dark grey. My ears were ringing (I lost part of my hearing, and got tinnitus from the blast) Pain was distant... Adrenalin probably diminished my feelings of pain, as we seemed to have been left for dead in hostile territory. We could only see about fifty meters, and our thinking was "fuzzy" but our medic began rendering medical aid, and the Lieutenant and I got M4 carbines and were providing security.
So, my experience is on "both sides of the line of heroic fiction" we were capable of combat, and other forms of action (rendering medical care). I don't know if we could have operated technical gear, our NVG (Night Vision Gear) was broken; our radios had been knocked out of their mounts and were damaged; the batteries for the vehicle had exploded, so there was no electrical power for the radios.
The rest of our patrol and the EOD Team we had been escorting believed us dead (no activity and couldn't get us on the radio(s); so they weren't risking lives for the "recovery of bodies" so it took at least 10 to 15 minutes for them to reach us after we regained consciousness. (I have been trying to get copies of the unit radio logs for years.) They were checking for more IEDs and other threats.
Once we were protected by our fellow troops and the QRF and Recovery Team (Recover the vehicle, other gear, so it doesn't get taken by enemies; recovery of wounded and/or bodies) we began to shake. Our Lieutenant's hands were shaking so bad he couldn't light a cigarette. One of the QRF or Recovery Team lit cigarettes for all four of us, and I smoked one of my few cigarettes ever. (I am opposed to nicotine does have some beneficial and perhaps psychological effects.)
Giddiness overwhelmed us, and we would giggle with minimal prompting. I could feel a headache, and was (probably more than) a little uncoordinated.
I rather vividly recall the 30 to 60 minutes after we woke up at the scene of the attack. I cannot recall the 60 minutes or so while we were transported to the BAS (Battalion Aid Station) {People who have had a TBI/knocked unconscious should NOT be allowed to sleep for at least 8 to 12 hours! At the BAS our physical wounds were attended to (somewhat) and we were give Percocet (as I recall) and let to go to sleep! (WTF!)
Our Chain of Command was "desperate" for "Boots on the Ground" and instead of being allowed to recover, within 24 to 36 hours we were back in Combat! MADNESS! Foisting Drugs on a soldier with an M-4 Carbine, and putting us in combat! We were a Danger to ourselves and our fellow soldiers!
Treatment for TBI/Concussions is well understood; more so now, but GD!
I mention this because in real life, and so (possibly in fiction) some people can be K.O.ed ("knocked Out") and still function... Well practiced actions, such as use of a rifle or other weapon, and other combat drills were much easier than conversation, or cognation. My hearing was significantly effected, and I don't think I could see clearly beyond 300 meters (my glasses had been damaged, although mostly protected by the ESS goggles that stopped most of the fragments, and slowed down the rest).
I had served more than 20 years in the US Army, and so most combat drills were "instinctive" they say some 10,000 repetitions may make an action rote. Tactical weapons handling was something that the units I was assigned to (and thus I) di for more than 10 hours a day, some 100 days a year (10,000= hours a year).
So, a character might be able to use a pistol, or fistfight, but have difficulty picking a lock, or noticing subtle clues.
According to my medical records I have experienced at least 14 TBIs, and I have volunteered for several studies involving the treatment of TBIs. I have also studied a lot of material about the treatment of TBIs, and dealing with them afterwards.
YMMV ("Your Milage May Vary). As the person who fell off a semi-truck mentioned losing (or diminished) sense of smell. I have had friends undergo significant personality changes (possibly effected by emotional responses in addition to the physical injuries), and other effects.
Excellent Question, and some very good answers in numerous posts before mine.