he has been in my tank for about 10days now and 2 nighs ago my father accidentally turned off my heater and filter

, the morning after I found that the temperature had went down from 27C to 21C, and I also found my male sword tail lying on the gravel, but not dead. While the female is ok, he was acting weardly. He went up to the top of the tank and was swimming against the filter's water stream without changing location, just moving his head and tail. When I fed them he just ate some few flakes and went up again swimming against the water stream. About an hour ago he went down on the gravel and I found him dead with one very red and infected eye. Is this an infection which can affect my other fish?? What should I do?? Thanks for your help