HELP ASAP!! My betta fish is laying at the bottom of it's bowl with one fin up!?

I've has this fish for only two months now. I have been on vacation for two weeks and my friend was suppose to be watching it but when I got back her bowl and my other fishes bowl were foggy and seems dirty. My other fish is fine, but my other betta in laying at the bottom, seems lifeless no gills moving and it little fin was kind of moving. As soon as I saw this I changed it's water as soon as I could. my friend sAid she she did feed them every other day. SOMEONE TELL ME WHAT'S GOING ON!!