Why is my betta fish laying sideways and what can I do to help it?

A betta fish laying sideways may be a sign of swim bladder disorder, which can be caused by overfeeding, poor water quality, or stress. To help your fish, try fasting it for a day or two, then feeding it a pea without the skin. Ensure the water is clean and at the right temperature, and consider adding aquarium salt. If the issue persists, consult a veterinarian or a fish expert for further advice.