So, we spend the day moving and grab some lunch, and then it's around 2:30 or so, and the fish tank is still out there - except now it's sitting in direct sunlight. I go and check it out, and the poor fish is struggling to stay upright, listing back and forth. Not a good sign, so I grab the tank and bring it in. The water is very cloudy (think muddy stream water), and earlier in the morning, the fish had been gulping for air at the surface, so obviously the water has been around for quite a while and is de-oxygenated. I then fill a pot with some tap water, imagining I'll let it sit for a few hours, let the chlorine evaporate off, and then swap out the water.
I check back on the fish about 30 minutes later, and I see the fish floating on the surface, sideways. Fortunately, it's gills are moving, so I decide that it's got to move to the clean, cool water, even if it's got chlorine in it. Once the fish hits the water, it seems to be doing fine, swimming around. So, I go ahead and clean out the aquarium, rinsing all the gravel, and filling it with clean tap water. Now it's just sitting, and I'll move the the fish from the pot to the tank in a few hours.
Of course, what this really comes down to is the girl next door doesn't have a clue about fish. For the water to get that cloudy in a week or so means she's probably been over-feeding the fish like mad. Oh well, hopefully the little guy makes it through all this shock . . .