Betta. Sick? Brain damage? Swim bladder?

Question
Hey,
I have two veil tail bettas (in separate tanks) and until yesterday they were fine, acting normal and friendly. Yesterday my betta (that I have had for a week now) laid on top of his cave...it seemed as if his eye and side was sticking out of the water but he'd swim off of it and back multiple times. Today he would lay between the cave and side of the tank. I was worried so I changed the water like I normally do and he is still acting 'sick'. He now just lays at the bottom of his tank and doesn't move unless it is to swim to the top for air. When he does swim it's in 'jerky' movements and then it's back to the bottom he goes. He also floats a little to the top but then manages to stop himself.
Could this be brain damage? Swim bladder?
Please help me.  My bettas are very important to me.

Thank you!!
Brittany

Answer
Brittany,
No it isn't brain damage. I believe it is the combination of a tank that might be too small and I am guessing he does not have a heater. They are tropical fish and need their water to be at 80 degrees at all times. When the temperature drops below that, they start to get lethargic. That is what you are seeing now. Make sure he is in a tank no smaller than 2.5 gallons, where a 5 gallon tank is best, and that he has a heater. Once you do that, you should see a big change in him.