I recently transferred my betta back into his 5 gallon at my college. However, since it was winter break, I had to bring him home. The tank he is in right now has been running empty for a month. Before it was cycled, but since it has been empty, there are no signs of any ammonia, nitrite, or nitrate. My betta was doing fine the first two days that I moved him back in. Now he stays in his cave all day and breathes heavily; He has been like this for the past three days. He still came up to eat, but I have been fasting him for a day just in case. His tank is at a good 80 degrees with a heater and filter so I have no idea why he is suddenly so lethargic. I have never seen him like this before. Occasionally, he will come out if I stare at him long enough, but he just darts around the tank(somewhat erratically) for like 5 seconds and goes right back into his cave. Even thought there are no signs of ammonia ,I've still been doing 25% water changes daily just in case, but nothing has changed.