Good to hear they're back to normal, but that they are after a water change makes me suspect you had some ammonia in the tank, or nitrite. Both can do a lot of damage, which may be permanent. Hope not.. but get the kit and test regularly, until you are sure you have a routine in place that keeps the parameters stable all the time. Depending how many fish you have and what size the tank is, sometimes water parameters can go off pretty quickly, if something goes wrong.