!!!PLEASE HELP!!!

Question
I have a pretty and sweet goldfish named sophie mol, i've had her for over
three years with absolutely no problems until now.  recently she's been
getting very big, with a very long body and an even longer tail (ok, she's a
feeder-type goldfish).  currently she's in a one gallon tank (it's aerated).  I feel
like this tank is much too small for her, since she doesn't have much room to
swim around, and i really want to get her another tank.  about five minutes
ago i checked on her and found her floating belly up at the top of the tank.   I
got really scared and tore off the top of the tank and she immediately
snapped back to her regular self.. but obviously, i'm EXTREMELY worried.  
could the small tank size have caused this? is it a disease? what can I do? we
are moving to a new house in less than 40 days, so i'm a bit wary of buying a
bigger tank just yet if it's really a disease that's causing this.  i don't know
where she would get a disease though, she's the only fish that's ever been in
that tank, and she's always been healthy.  PLEASE help!!! i don't know who to
ask.. i can't lose her. please please help!!!

Answer
Ok she sounds unhappy i would get a 20 gallon long tank because those fish get pretty big. I would move her into a bigger tank because goldfish produce alot of waste and the ammonia is killing your fish is what it sounds like. I would change the water at least once a week and when you can get a bigger tank get a filter,light,and decor. and other things you would like to put with her is up to you. Also i would not get anymore fish until you figure out if your tank is big enough with your petstore because i don't know the maximum size sorry.