It woke up, and now it was the goblins' turn in initiative.
Here's where an artifact of group monster initiative came into play: The wounded goblin stood up, slapped the face of the sleeping goblin next, disengaged, and fled into the chamber where the goblins were rallying. The slapped goblin did the same thing. So did the next one, and the next one. Essentially, the work of the sleep spell was undone by monsters all acting on the same initiative. ... what I found interesting was how the sleep spell was undone essentially because like monsters all act on the same initiative. This would be much harder for PCs to pull off, I think, if the situation was reversed since they act on different turns, often with monsters in between.
Have you seen a situation like this unfold in your game? What other sleep shenanigans have you seen play out?
Yes, I've seen things 'chain' like that, before. Often in the player's favor, as well as the monsters. It is an artifact of turn-based cyclical initiative that sometimes a thing one creature does can be completely un-wound before it's turn comes back again.
But, yes, monsters all going on the same initiative is a convenience for the DM, and when it does make screwy things happen, it helps to think how they'd have to manage it were it not for that convenience. For instance, in 3e, we'd often have groups of monsters move into flanking positions, then all attack - that's doable, you just move into position and ready to attack as soon as your ally flanks. It works even if the monsters all have theoretically separate, but very close, initiative. The issue I see with the waking chain of goblins is that it doesn't work quite so conveniently if they just had very close initiative - what if the one woken had the lowest of their very close initiatives, for instance. Since the whole point of the convenience of having them go at the same time is not to actually have to keep track of that, you can't really know.
Another system artifact that enabled the effect you saw was the treatment of movements & actions in 5e: getting up is just some of your movement, and you can (in a pretty small room, I guess) use the rest to reach an ally, action to slap them, and continue to move through a door (object interaction to close it) - goblins in 5e get to Disengage as a bonus action, too, otherwise the first one moving away from the cleric to wake it's buddy would have provoked. In 3e or 4e, the newly-woken goblin would have used it's move to stand up, and, maybe, 5' step & it's standard to wake an ally w/in reach (in 4e, give the ally a save) - they couldn't all have woken eachother, /and/ all fled, because the move action was discreet and Opportunity attacks a little harder to avoid.
The 5e method of movement (and only one reaction &c) is intuitive and makes the action seem less 'jerky,' but it's still going on in a turn-based system, and that jerkiness is there for a reason.
