Bloating of Flowerhorn stomach

My Flowerhorn which has been happily growing in my tank for up to 3 years I just woke up this morning and saw that it is now swimming upside down at the bottom of the tank and now it has arrested completely on its side at the bottom of the tank I have no idea what to do please help me this fish means a lot to meNo strange behavior before this every 15 days i change water but i was late to change it and the strange behavior started
it has been 1 week since this happen and it didn't eat any food water now is in peak condition only half tank of water is kept in dim light
I added espom salt
Now condition is severe

Hi and welcome to the forum

I can't tell anything from the pictures. If you could post some clear pictures or a 1 minute video, it might show more. You can upload videos to YouTube, then copy & paste the link here.

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If a fish suddenly bloats up overnight and stops eating, it is usually terminal.
Did the fish do a stringy white poop when this happened?
If yes, then it has a bad bacterial infection in it's body and there is no real cure.

Once a fish stops eating and or can't swim properly, that is usually the end of it and the fish should be euthanised.