Bettas are one of those fish that lack lids on the eyes. So you'll never see them close their eyes when they sleep. They still need to rest and regain their energy stores, though. And while it may seem like they're always adrift in the water column, they DO sleep. They utilize their swim bladder to control their depth in the tank. This allows them to hold still in the middle of the aquarium, sleeping happily. Unfortunately, if they develop swim bladder disease from overfeeding, it can impair their ability to control their buoyancy. This is why it's essential to regulate their feeding closely to keep these fish healthy.