Drowning looks like one of two things: Either you are trying to catch your breath every time your mouth comes above water, and it's happening so infrequently that all you can do is work on inhaling and exhaling. And if you're not breathing at all, you obviously, physiologically can't shout or speak or do anything. But either way, you're not able to shout or yell or call for help or say anything. You have no choice in the matter, like your body has taken over. The whole point of that is to keep your head above water as much as possible.