I had a nasty case of concussion after a bike accident. I kept repeating myself immediately after the accident but all i can remember is coming round in hospital not knowing what the heck was going on. earliest thing i could remember before the accident was about 6 months before it happened!!
gradually over the course of the day my memory came back but like the OP i felt very groggy, thoughts were confused and i kept feeling like i'd pass out any minute. i was so worried i'd not wake up that i called the nurse using the button but that didn't do much good as she spoke french, then i remembered i was on holiday!
anyway, i did wake up and was basically fine although kept having flashbacks for a month or so.
i was wearing a helmet too, but it wasn't full face so didn't do very much as it was mainly my face that hit the ground.