Fish Playing Dead

[qoftheq]

So, today around five or so I went in to feed my fish (4 corys in a 10 gallon tank) and one of them was upside down, pale, and not moving. I had to go, so I came back a few hours later to change the water and remove the unfortunate cory (and mourn, I was actually very sad about this) and the fish was still in the exact same position. I started messing with the filter, and a few minutes later I noticed he was right side up and still not moving. I attributed this to the change in the currents of the tank due to the filter and kept about my business. A few minutes later I noticed he was a few inches away from where he was before, and so I tapped on the glass. He turned and swam away across the bottom of the tank! He seems okay now, although he does seem a bit lethargic at the moment. What is this? Do fish play dead? He gave me quite a scare!

 

[QuotheRaven]

Sadly it may be on it's way out as most fish soon before there death swim on odd angles act very lethargic and there colours fade.
My cories do rest so your's may be just sleeping.

 

[qoftheq]

Is there anything I could do? Or do I just have to let nature take its course from this point?

 

[QuotheRaven]

Well what are the water stat's??

 

[qoftheq]

I accidentally messed up the biological filtration system (I know, I know, I've mentally smacked myself many times for this) and so the ammonium is pretty high, hovering around .50 ppm. The nitrates are low and stable, nitrates are in the safe zone. The pH is 6.4, fairly soft water and low alkalinity. The temp is 78-81 degrees farenheit w/o a heater. My room is fairly warm, but I'm trying to cool it down because I know this is a bit warm for them. I'm doing 10-15% water changes twice daily and testing all this once daily. Other three fish seem to be just fine.