When getting naturally effected by miningfatigue, the player gets shown a Guardian face on the screen, while swimming this face is not in position to the players head and will therefor look a bit odd. It is not the fact that the face in out of position when you are in F5, but the fackt that it is not in sync with the body when you swim in the water....

Sorry for bad English 

(The screenshot is taken in F5 to show the position of the face)