Rooster with Balance Issue
Is he getting enough water and food, or could the others be keeping him from those? His inactivity and sleepiness may be preventing him from drinking enough, and dehydration can cause balance issues. Another possibility is an ear infection that is making him lose balance. Have you added any new birds recently that might have been a carrier of Mareks disease? Does he have any nasal drainage or watery eyes that could indicate a respiratory infection? I would place him in a crate with his own food and water for a few days, and add some vitamins and electrolyte powder to his water. Feed stores sell several brands for chickens. Check his crop to make sure that it is emptying overnight and not sour or impacted. Look his skin over around the vent, neck and under wings for lice or mites.