30 minutes ago, I dropped my betta Jerry while cleaning his bowl. He fell from about 3.5 ft on to tile. I quickly (and gently) picked him up and put him back in his bowl. He sunk to the bottom on his side. He can move his fins, and he is breathing, but he cannot move his body. I'm extremely worried as this fish has a lot of senitmental value to me. I put him in a dark room and made sure his water was warm. Am I correct in assuming he might have a broken back? If so, should I wait to euthanize him, or do so immediately? And if I did have to euthanize him, what would be the best way to do so?