Help! Think I'm about to lose my special little Jake :(

Some of you will probably remember him, he's my lovely little leucistic with the extra leg. When I got him and his brother they were both in poor shape, after a little while they both flourished. Put weight on, beautiful fluffy gills, etc.
Well Jake has been looking super skinny for a long time, he's been eating but only bloodworms, he refuses anything else. Last night I'd had enough so I scooped some water from the tank up into a 4l container and put Jake in there. I popped a cube of bloodworms in there before I went to bed, he ate about 3/4 of them so I left the others, hoping that he'd eat them as well.
I've just come down to see my poor little man floating on his back. I thought he was dead, picked him up and he wiggled a bit so I put him in his tank hoping he'd be a bit better there but he just sank upside down to the bottom
I put 1l of bottled mineral water in a tub and I've put him in the fridge in the hope it will help him. In the mean time, does anyone have any ideas?? Don't want to lose him

Lower the water level (if you haven't) to just covering him. This should encourage him to stand on his feet and make it more difficult to flip to his back. Keep him fridged for a few days. Hopefully, keeping him cool and dark will destress him. Good luck!