The fish would be gasping at the surface if there is a lack of oxygen and/or from ammonia poisoning, all of which could happen from the filter not working.
Usually in just that amount of time, it would more likely be the lack of oxygen since there was no more surface agitation.
But if the tank is really overstocked then ammonia toxicity might be possible.
It's sort of already too late since it's been some time since it happened, but for future reference, as soon as you notice the power is out, try to increase dissolved oxygen as much as possible (surface agitation from filter current, air stones, powerhead, etc., even agitate the water by hand if necessary). A cooler water change could even help (colder water has more oxygen, and it is new cleaner water, but I would increase aeration before doing water changes as this is a bit slow and probably more stressful on the weakened fish).
When a fish is on the edge of death from suffocation, it is normal for they to have a hard time staying upright, so this is not a good sign and you need to help it get oxygen ASAP. I had a Arowana jump out of the tank when I was not home, I got back and he was really dry and nearly almost died, but I placed him back in the tank, and help him upright underwater while running a airstone directly under him to get as much oxygen into his gills as quickly as possible. I was a little worried about the air bubbles going inside of it's gills, but my options were limited and his time was running out so I had no choice, well he is still alive to this day and is 110% healthy! I was really worried, he was so dry and his eyes were even dried up and sunken in, he didn't look like he would make it even with my help, but glad he did.
So for that fish having trouble staying upright, just provide more oxygen and give him time to recover, I doubt his swim bladder is messed up. Haven't heard of bloating as a result of suffocation though (unless maybe it is a fish that is a known "air" breather and it gulped a lot of air, which I still haven't heard of bloating, but I guess sounds possible).
But anyways, keep an eye on ammonia levels incase some of the beneficial bacteria on the media did suffocate as well.
Not 100% positive cleaning the filter out was the best thing to do unless it was super dirty slowing flow and just a bunch of collected waste. I would of been worried of upsetting the cycled media with drastic cleaning after already going through the power outage.
Just keep the aeration going and watch the ammonia/nitrite levels. If the ammonia rises, stay on top of water changes for a while until the fish have had some more time to recover from the initial near suffocation.