Is my Fish sick? HELP URGENT?

Even though you say your tank is cycled, it's pretty easy to upset the balance in such a small tank. If you can test the water, I'd do that. Otherwise, I'd start with a 50% water change, using a good dechlorinator and water that is the same temperature. These are hardy little fish and that's a fairly small tank, so the first thing I'd suspect is a water quality issue. They can go a few days without eating, but it's easy to foul the water by over-feeding. Change the water and they should perk up pretty quickly. The fish stores always want to sell us medicines, but frequently the very best thing for improving a fish's health is lots and lots of clean water. If the tank is new, ammonia and nitrites can build up quickly, poisoning your fish.