What I wonder is, if you don't have any control over your own movements anymore, how likely are you to also drown the person that is trying to save you? Is that something that can happen?
You'll notice that lifeguards usually approach from behind the person that needs rescue. The standard response is to grab anything that can help the drowning person stay afloat, which includes the rescuer.
Don't punch them, it's less effective and can knock them unconscious, which can complicate the rescue.
Source: was a trained and certified lifeguard and swim teacher in my teens.