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.
Best Answer
To tell if someone is sleeping rather than unconscious:
There are limitless ideas for you to play around with. I think the most natural are shaking someone, or talking to them. Those two cover the vast majority of my experiences in real life and in media.
Forcing your players to play suboptimally is not fun for them
Most people find doing well to be fun. Yes, we all like to do something silly or flavorful sometimes, but that should be the player's choice. Being forced to do something that you know is bad or wrong sucks. It feels like you are being cheated or tricked.
If it's important, you do it
I don't know about your players, but mine don't fuss over the details. In that situation I would fill in the details; "you hear character snoring and run over to shake them awake" or "you see character sleeping peacefully and run over the wake them".
This isn't the right time for skill checks
The player already has the knowledge, you are asking them to justify the reason for having that knowledge. Gating that behind a skill check doesn't make any sense. We already know whatever method the player used has succeeded.
The player knows the character is sleeping, just let them have it even if you can't think of a justification.