I assume this is the 24 gallon tank?
You've got 10 fish in it? (well now 5 with the losses?) I'll be a box of donuts (and I value nothing more than donuts) that your problem is right there. You've got way too many fish for a tank that size. I'm willing to bet that you'll measure ammonia when you test your water. Ammonia makes it hard for fish to obtain oxygen, and they will move slowly, and gill rapidly.
Plus it sounds like a few of the fish died, and you were unable to remove them from the tank, right. In a tank that small, I think that could be a real problem too, probably causing transient ammonia spikes.
A tank that size should probably have a max of 4 small fish.