I did a 100% cleaning of my betta's 5 gallon tank yesterday which I do weekly since his tank isn't filtered, and ever since he's been acting strange. He sits at the bottom of the tank when he used to always hover around the top, especially around his heater even though the tank is kept at 78. He's constantly hiding away too. He used to never use the little house I have in there with him, now he's constantly in it, or hiding behind plants. He interacts with me as usual, though. Whenever I look in at him, he'll swim to the top, and swim around like usual. But when I leave, he goes back to the bottom. There is no physical signs of illness. He's eating normally too. I don't want to do another water change because I think he's stressed, and I don't want to scare him more. I think he might have temperature shock because I did find the water he was sitting in a little colder than usual, and I only realized that when I was putting him back so he was in it for about half an hour or so. His tail got a tiny split in it too from being transferred. I just don't know what to do because I don't know exactly what's wrong with him.