I had a young chook with same problem I bought in a load of chicks for growing on for meat, and for some reason my Polish decided to pick on this particular one and started pecking it terribly - mostly around the head and neck. If I hadn't got to it she would have killed it for sure. It was disorientated and falling over - I wrapped it in a towel (chook about the size of my hand) and actually put it in a tupperware jug so it couldn't move or fall over. It slept for about 12 hours - I gave it drops of water and a little food which it took ok, but it was very happy where it was.
It took a leap from the jug but wabbled everywhere, so I wrapped it again and put it in a small box for another few hours. In the end as it became steadier on its feet, I put it in the cage with some very young chicks, where it wasn't challenged, and after a few days it made a complete recovery. For those few recovery days, it kept sitting back - would stand and sit again. It took about five days to be strong on its legs again.
Shock more than anything I think. Be patient, keep it quite and still and just keep an eye on it - give it a little water on a spoon or bud and a bit of food from time to time and it will hopefully be fine.
Good luck.
Kate