If it was a change from 78 to 80 that is probably not the issue. If it is 78 to 82 it could be more of an issue as 4 degrees is quite a change. The reaction to going into shock would have been different though. He perked up after the water change so it is obviouse there is some other issue. All I can really say is what I have already said before, to make sure he water is clean whether that is to just change it frequently or get the test stripes and do it when it registers a stressed level. If you start to see other symptoms like for bacteria or fungus then that has a whole different route of what you should do.
Edit: Maybe he like his temp at 80 and is cold and lays at the bottom when it gets cooler. Just a thought?!