Another sick oscar

[Carolinasculpture]

Hi! This is my first post. Have just joined due to our daughter's oscar's health issues, we are looking for any advice.
Background: he is about 3 years old, in a 75 gallon tank with a gourami and a dragon fish thing (both around 3 inches). Two hang on back filters and an air stone. Small gravel on the bottom of the tank, not much for decorations. Tank is around 78 degrees. We usually exchange about 20 gallons per week. Have had no problems with parameters in the past.
So, we went camping for a week over spring break and came home to a stench in the house. Quickly found out it was the Oscar tank. The filters were caked with food and of course ammonia levels were through the roof. He had been grossly overfed by the same person who had always cared for him in the past. He was lying on his side on the bottom of the tank, watching us.
We immediately began to change out the water and remove all the food we could see. Did a 75 percent water change that night. Next day, changed about 50 percent and vacuumed half of the tank. Did the same the next day. Finally had much better water. After a few more days he started to swim a bit and eat some. Then, he managed to jump out of his tank at about 2am. We heard him and put him back in. He got a good scrape on his side. Now he floats on his side at the top of the tank. He tried to swim from time to time and seems to have to work hard to swim down and get his body straight.
Swim bladder issue? Ammonia poisoning? All the above? Anything we can do for him? Do you think he can get better?
Sorry this is so long...thank you for any help!
Edited to add, we did use melafix for the scrape.