Can visual inspection tell the reason a creature is unconscious? Is there a difference between a creature that is sleeping normally, sleeping magically, or unconscious due to dropping to 0 HP? Does a stable creature at 0 HP look or behave different to an unstable one?
This came up in game last night after a character in darkness cast sleep on themselves. Another character moved to the unconscious figure. The player said "I shake them awake". My question was, "How do you know they are sleeping? They might be at 0 HP, in which case wouldn't the appropriate action be to use Lay on Hands?" Generally, if someone is unconscious in combat its because they have gone to 0 HP, in which case the usual course of action is healing magic or a medicine check to stabilise.
In short: The paladin saw an unconscious friend. Can they, without an Action, determine the cause of unconsciousness?
Since we are all at the same table, the players all knew that the wizard cast sleep at ground zero and put themselves out instead of their foes. However, the characters were far enough away that ingame they did not know what happened. All the paladin character knew was that they moved to within darkvision range and suddenly saw their friend unmoving on the ground. This was in combat, so the action economy was important.
It seemed to be bad metagaming for the player to pick the Action "shake the character awake" instead of "do some healing magic" or "stabilise" or "drag to safety" or something else.
I ruled that there is no perceivable difference between a normally-sleeping unconscious creature and a magically-sleeping unconscious creature and a at-0-HP unconscious creature. All are unmoving, and unresponsive. All are breathing and have a heartbeat. In the case above, the wizard had been wounded, so "lack of wounds" could not have been a clue.
My players disagreed. I'm unsure if my ruling was right.