How long do concussion symptoms last?

My dad was out ice fishing about a month ago when his friend found him outcold on the ice with his tongue in the back of his throat and his eyes rolled back. My dad is super stubborn and of course refused to go to the doctor. Today he told me that when he rolls over in bed he gets dizzy frequently and both his sense of smell and sense of taste has diminished. How long do concussion symptoms last and are these common symptoms?