Upside down Fish

Question
Two of my fish have been swimming upside down after i noticed that the air/water filter stopped working.  It was about hours  after my mom and i found out that there was no oxygen going to the fishes. One of my fish started swimming right side up but the other one is still upside down.  I read other questions saying the fishes would be upside down if there was gas in the belly but if the fish didnt have oxygen for a long period of time; was that the reason that caused it? and if so, does that mean my fish will die?
and is there anything i can do to save my fish?
P.S. my fish tries to go right side up but when it does, it leans on one side and turns upside down again (i think the left side of its fin is weak) HELP ME PLEASE!!!

Answer
As I do not know what type of fish you have, I would definately do 2 things.  First, replensh the oxygen flow via airstone or other filtration.  Second, I would do a 50% water change using dechlorinated, dechloramined and de-ammonia water.  This will improve the chances of your fish.  

If you can give me tank specifications, as well as water temp, nitrite, nitrate and ammonia levels, I can help even further.  What type of fish do you have?  How many?

Hope to hear from you soon.

Sincerely,

Adrian