why do you think it has gill worm? pictures?
for right now, you can make sure your water parameters are good, water change if needed...if in big tank, separate into hospital tank...
make sure water is aerated, raise temp.....
i always add salt, but that's up to you...
my midas had a fight and got stressed, he only used one gill for a while... wouldnt assume anything until you know the water is perfect and nothings stressing him, good luck...