I've had that happen with Fauna before after I kept talking to her (because she's so adorable) If you were talking to her a lot at a time then that might be why.
Omg that happened to me once but after tangy finished talking to another villager. I've only ever seen them get happy / angry / sad after conversations, but Tangy was like contemplating things and doing that "..." bubble. I definitely didn't talk to her at all before I saw her do that. Idk or maybe I'm remembering this wrong, but it was weird.
I've never known it to and I spend a lot of time over talking to mine when I'm trying to find a mover they just have nothing else to say for a while but they will be fine in a few minutes. Just like after they get angry or upset over something they won't have any dialogue for you until they return to normal