i don’t know if yours is a tiger variety but i see nothing about them sleeping upside down
https://www.aquariumsource.com/tiger-shovelnose-catfish/
mine actually swim upside down. they do not float at the top like yours
from what little i can see your fish appears to be ill and perhaps at the top where the water quality may be less toxic or more oxygenated
it’s pretty hard to get a wild caught fish to eat aquarium food.
does it eat well?
is your water quality tested?