The only reason fish will act abnormal after a water change is if you did something drastic to the water conditions.
With small water changes its not that critical. With large water changes, you should be replacing water with just about what was there (as far as temps, chemicals, etc...).
Was there a temperature difference in the new water?
How about salt?
Prime, stress coat, any water conditioners?
One time I drained a tank 50%. I threw a python in the tank pumping water in that I checked the temp with by feel. Normally, I add salt, prime and stress coat to the water prior to putting it in the tank. This time I didn't and I payed the price too. I lost 3-4 tiger barbs, a few danios and an electric blue dempsey. I musta shocked the **** out of em and they just couldn't handle it. That was a hard lesson learned.