I have a male double-tail betta. It's a very beautiful and healthy-looking fish, and eats very well. He lives in a filtered (not heated, no petshops around to buy a heater anymore, but I will work on that at a later time) three gallon tank with live plants and moss. His environment seems great.
The behaviour I notice is that he tends to lay down a lot, sometimes at a small angle on his side (kinda like / ). When I come closer to check him out, he usually gets very active and hyper, darting about and flaring at his reflection. But other times, he just sits and seems to almost be gasping. The tank parameters are fine.
Besides this, nothing is wrong with him. I just want to make sure he's alright; he's a very bright purple double tail betta with a great personality! :)