The question “NPC casting Suggestion on PC: who decides it's reasonable?” gets at the issue of who decides what is reasonable when a Suggestion spell is cast.
Other questions try to get at “How do I decide what is a "reasonable" Suggestion?” – but the level of abstraction of the discussion seemed to leave it as relying on too much opinion to have an allowed answer.
As a result, we are attempting to ask a question on Suggestion for a specific scenario to see if a more definitive answer can be reached.
We recently faced a band of five Yuan-ti which can cast Suggestion 3x per day. The DM used this cache of fifteen Suggestion spells to tell our party over multiple rounds to “sleep” in order to capture us. It was overwhelming. We didn’t have enough Counterspells and Dispel Magic spells to resist.
In an upcoming session, our party is soon going to enter the Yuan-ti’s lair. It is almost inevitable we will face this tactic again with even more Yuan-ti with even more Suggestion spells. In some ways, we were lucky last time because the Yuan-ti let us escape. This time, they won’t let us live. There is a risk of a TPK.
Suggestion as a spell says that the action must be considered reasonable.
Is the Suggestion to “sleep” during combat ever reasonable? Technically a PC probably cannot fall asleep at will – so the PC will simply try to sleep – but the effect is the same in that they are taken out of combat.
Adding to that risk is the inability to reverse it even if the risk increases. Jeremy Crawford has ruled that the suggestion only has to be reasonable at the time it was cast. Thus the PC will be trying to get to sleep until they can for up to the next eight hours (see Sage Advice).
Is there agreement that Suggestion can always be worded in such a way that it is reasonable for a PC (or NPC) to be taken out of combat (i.e. despite definite risk to life and limb) by trying to sleep?
Or is there agreement that in all cases where a clear connection between definite risk to life and limb can be drawn that a Suggestion to try to sleep is not reasonable? (In which case – we can rule out that “sleep” is a reasonable Suggestion during combat.)