After switching houses to sleep for the night things still weren't improving. At 10pm we called Medical back and by midnight they were at Ross's site, and by 2am he was in the Peace Corps Medical office getting treatment to stop the dry heaving.
At this point we're still not sure what the problem is. Thank goodness PC is taking care of him, though, and they let me come along to make sure he's ok.
Lesson learned: the importance of the "locator form". That makes emergencies like the one we had much easier!