Betta Fish: Help with my betta

My betta fish is acting strangely; he seems to have more difficulty swimming than usual. When he stops, instead of floating, he sinks, and he's spending more time at the bottom of the aquarium than normal. But other than that, he doesn't seem sick yet. Also, he's swimming less gracefully than before, with his rear pointing downwards more. He's also not flaring when I stimulate him. Does anyone know what it could be and how to treat it?. From my research it seems to be a problem with the swim bladder, but I wanted to confirm this