It appears Gyarados got stuck on a plastic plant at the bottom of the tank. The plant has been removed as well as another it came with. He did not eat the following morning, but did start eating about 24 hours after the incident. The rest of the info can be found below.
What size is your tank?
What temperature is your tank?
Does your tank have a filter?
Does your tank have an air stone or other type of aeration?
Is your tank heated?
What tank mates does your betta fish live with?
What type of food do you feed your betta fish?
Aqueon Betta Food & Dried Bloodworms (once a week).
How often do you feed your betta fish?
Twice a day.
How often do you perform a water change?
What percentage of the water do you change when you perform a water change?
What type of additives do you add to the water when you perform a water change?
API Betta Water Conditioner.
Symptoms and Treatment
How has your betta fish's appearance changed?
Left pectoral fin is damaged.
How has your betta fish's behavior changed?
A bit lethargic, wanting to hide more, no longer coming to the top when we open his lid for feeding time (but will come once we have dropped the food in and is eating) and being much more fearful of activity around his tank.
When did you start noticing the symptoms?
Have you started treating your fish? If so, how?
Yes. API AQ salt.
Does your fish have any history of being ill?
How old is your fish (approximately)?
Maybe 3-4 months (wild guess).