Sans's will come up as him just being purely exhausted - like someone who has just pulled an all nighter, or gone for a very long series of runs. He isn't hurt or damaged, but with the way monster physiology works, the lack of strength in his spirit at the moment makes him physically vulnerable and weak.

He does probably just need to sleep, though. Though that dreamcatcher landing on his chest seems to be what wakes him up just enough to process where he is. One socket cracks open, dull blue light shining from within.

"Just tuckered myself out," he slurs, like he's trying to answer a question that he's not even sure was asked. It was probably asked, right?