Having a weird problem with some of my female Bettas but I'm not sure it's actually a disease. The "symptoms" only appear in one Betta at a time, too. There are no physical signs of anything wrong, the sufferer just appears to be sleeping, usually at the bottom of the tank, and sometimes nose down. If she moves at all she appears to be sleepwalking and her breath is almost undetectable. All water tests have come back 0, 0, ~20 though in one case the comatose girl seemed to wake up after the water change. Sadly that one managed to jump out of the tank that night Otherwise they just seem to sleep to death.