My fish fell out of the tank, now on its side. What should I do?

Oh goodness. It sounds like she was pretty stressed during the event. There isn't much you can do but give her some time to see if she can recover. Make sure your water chemistry and temperature is optimal. I hope she does ok. Wishing for the best!

Check water chemistry first. Use a home test kit or submit a water sample for testing. Aim for an absence (0 ppm) of ammonia and nitrites with nitrates at 20 ppm or less. Perform a partial water change to stabilize water chemistry and/or to improve water quality. Use only conditioned water that is temperature matched to prevent further stress or shock. Bettas do best between 78 F and 80 F. By your description, the issue may be swim bladder disease. This can be caused by infection (bacterial or parasites) or constipation. Maintain water quality as described above. Fast the fish for 3 days then resume feeding bits of cooked and shelled green peas. This will help with constipation. If this doesn't help. you can get a broad spectrum antibiotic from the local pet store. Look in the aquarium section. Follow label directions carefully and remove the carbon filter insert during treatment.

Checking your betta's environment is always a good first step- test the water, make sure the tank is the correct temperature, you're not overfeeding, etc. If he is doing headstands, it is possible there may be a swim bladder issue (the part of your fish that helps them to move around and stay buoyant in the water). Looking up swim bladder issues may give you more information about the possible cause and treatment.

He is "old" for a Betta. Check the water chemistry and temperature. You can use a home test kit or submit a water sample for testing. The local Petco may do this for free or for a small fee. Aim for an absence (0 ppm) of ammonia and nitrites with nitrates at 20ppm or less. Perform partial water changes to stabilize chemistry and/or to improve water quality. Use only conditioned water that is temperature matched to prevent stress or shock. Bettas do best between 78 F and 80 F. The cloudy eyes may be due to infection. Maintaining pristine water quality will help, but you may need a broad spectrum antibiotic as well. Look in the aquarium section of the local Petco for medication. Follow label directions carefully and remove the carbon filter insert during treatment if indicated. Even with treatment, there may be permanent damage to the eyes if the condition has been chronic. The "laying down" is sometimes seen even in healthy fish. They may choose to lay on gravel or the broad leaf of a plant. It may also indicate infection or injury though. If hebisbhavibg difficulty reaching the surface, decrease the water level to make it easier. Bettas need to surface occasionally to get some air.

Recheck water chemistry to confirm 0 ppm ammonia and nitrites with nitrates at 20 ppm or less. A pH of 7 is fine and they can adjust to more acidic water as long as the change is gradual. Temperature should range between 78 F and 80 F. Plain aquarium salt (NOT table salt or epsom salt) can be used as a general tonic to reduce stress, improve gill function, treat minor infection and aid in recovery. Dissolve 1 teaspoon of salt per gallon of water in a cup or two of tank water and gently pour it into the tank. Perform partial water changes every couple of days to maintain water quality. Treat only the volume of water being replaced. Treat with aquarium salt for no more than 14 days then reassess the condition. An antibiotic, such as kanamycin or erythromycin, can be found in the aquarium section of the local Petco if the salt treatment doesn't help. Follow label directions carefully and remove the carbon filter insert during treatment if indicated.

As long as you maintain pristine water quality via filtration and regular partial water changes, he should heal up. Use only conditioned water that is temperature matched to prevent stress or shock. Bettas do best between 78 F and 80 F. Consider a product, such as Stress Coat, to promote healing. https://www.petco.com/shop/en/petcostore/product/api-stress-coat-aquarium-water-conditioner

Confirm proper water temp. Bettas do best between 78 F and 80 F. Low temps may lead to stress and illness. You can also try a small amount of plain aquarium salt (NOT table salt). Salt can aid healing and acts as a general tonic. Use 1/2-1 teaspoon per gallon of water. Driftwood or Indian Almond Leaf can also be used to condition water.