Can you be in a coma and loose your memory after being shot in the chest if you're a 13 yrs old teenager?

Im writing a novel and for some reason,I just think that's almost impossible.I don't know if it's impossible,but it seems rare. So the real ques. is, if you are reading a story and a teen gets shot,would you think it's a little weird if he's in a coma for awhile and when he finallys awakens, his memory's gone. Do you think that's a little rare?