I woke up this morning and turned on my lights to my 75 gallon aquarium and I noticed my Severum was belly up, eyes a tad cloudy, and fins somewhat tattered. He was still alive and barely holding on, so I places him in a 5 gallon bucket with an air stone and his tank water. He died around two hours after the fact, but I thought he may have had a chance because he had a little more pep when I placed him in a separate bucket, but he was still rough. I was shocked and very confused because he was a perfectly healthy fish before this morning and overnight this happened. I just did a large water change a few days prior and all my other fish are in perfect health. The water is clear and clean and I don't over feed them. He was the king of the tank and never got picked on as well. Is it possible he ran into the glass and had brain damage? The last time I intorduced new fish to the tank was months ago so I ruled out an introduced disease. And help would be appreciated!