Sewer biodiversity, crab germs, and Ray's blood...

I think it's got something to do with her body temperature- she's a fire type, after all, and the process speeds up when she's in close proximity to 'em.

[He leans over and gently shakes Ray's shoulder.]

Hey, Sleeping Beauty. You wanna rejoin the land of the living, here?

[... No response. Venkman doesn't seem deterred.]

C'mon, Ray, I know you're not that tired.