why is my cory catfish not movin..

Brief：
i have a two week old 24l tropical fish tank community, with shoals of neons and danios, and an albino cory catfish. for the past day, my catfish has .. 

i have a two week old 24l tropical fish tank community, with shoals of neons and danios, and an albino cory catfish. for the past day, my catfish has stopped moving around, even for food, and just lies on the gravel breathing normally. i don't know whether it's ill, or lonely, as i heard you're supposed to keep corys in small groups. i don't know whether its injured, as when it does swim it swims very close to the rocks and so swims a bit lopsided anyway. im going to the pet shop tonight to buy some fish stuff and i wondered if anyone could offer any advice as to what is wrong with my cory. any helpful ideas will be greatly appreciated, thank you :)

Swimbladder is a disease which symptoms cause fish to become unable to swim correctly, your fish may exhibit swimming toward the bottom of your tank or bowl, then floating back up, swimming in circles or laying or floating on his side..

There are three main things according to the posts and articles I've read that can lead to swimbladder disease.

Constipation due to overfeeding

Bad water quality

Bacteria

Do a significant change when you suspect swimbladder disease and then follow this treatment. If you don't use aquarium salt this is a good addition to most tanks. The recommended dose is one teaspoon per gallon, or one tablespoon per five gallons. If you have never added salt and you are unsure; you may want to first acclimate him at only 1/2 tsp per gallon.