a sense of joy and then a panic

Wendigos. Larry Fessenden is OBSESSED with wendigos. He has his own concept of them though. They're like enormous blue vapor-mists with human bodies and deer heads, and they eat people, but from a distance it looks like a ghost herd. Quite cool actually. I'm assuming you've seen Princess Mononoke, and they look very much like the Forest God. And anyway they melt the entire arctic (or rather, the oil companies fuck up the environment, and then wendigos come out) so the last scene is of a character stepping out of an arctic hospital and hearing sirens and seeing the parking lot submerged in water.