This isn't too uncommon of a problem with power filters. (I was in the pet trade for about 10 years, and I had every major brand do it at least once.) It's likely that something jammed the impeller. It could have been a piece of carbon, some plant material, whatever. Since the motor is still trying to make the impeller magnet turn, but it can't, heat builds up and will cause the plastic or epoxy around the motor to swell, excacerbating the problem. It can get so bad as to scar the impeller. I had several of the first generation HOT Magnum impeller magnets swell and split. Sometimes we couldn't even get the impellers out of the motors to replace the parts. (This is pretty much the only model I've ever seen get this bad. I remember the rep explained to me that the impeller magnets on these were a rare earth magnet that seemed to be more prone to this kind of wear and tear. Not sure if that was true at all, but that's what he told me.)
It sounds like when you first removed the impeller, it dislodged the debris, but I bet there was still some swelling, causing the quick shut off. Eventually, everything cooled down enough to return to normal.
There's no real prevention for this. Just make sure when you do your tank maintenance you remove the impeller and get any debris out of the hole where the impeller sits and remove any plant material from the impeller shaft. Also, be sure to check after any power outage that the filters come back on. That seems to be the worst time for it to happen in my experience. If you have a filter (or pump for that matter) jam, try to let it cool before you plug it back in. It seems like having the motor plugged in while the impeller is jammed causes the magnet to lose its charge, making it more likely you'll need to replace the impeller.
