Hmmm, interesting.
I would like to question the writer on some of my observations though.
Ocassionally I have forgotten to turn the heater back on after a water change, several times in cold weather. We don't keep the house at tropical temperatures. The kitchen is kept colder than the lounge, and even the lounge is only heated during the day, at night the temperature drops. It is the lounge heater I usually forget (the plug is out of sight but the kitchen tanks' plugs are easily visible)
The last time I forgot to plug the lounge tank's heater on, it was 4 days before I realised
The temp had dropped to 19
oC. I had been wondering what was wrong with my fish as they'd started behaving differently. Instead of being out and about, they were all hiding or lying on the bottom. I'd even got as far as testing for ammonia and nitrite to see if they were to blame. It was only when I put my hand in the tank to rescue an upside-down nerite snail that I noticed the water was too cold. I turned the heater back on, and the fish slowly returned to normal.
In view of the article Colin linked to, was the 'odd' behaviour the natural behaviour, and the 'normal' behaviour a response to water that was too warm rather than the way round I had assumed?