Is my fish dying

I have a tiger  oscar that  I have had for over five years. In fact it was was first fishwhen i decided to get into the fish tank thingie. In his tank is also another oscar that has a big spot on it's tailfin whom I call spot.together the share a 55 gallon tank and have been together for alomost four years. A couple of days ago I noticed that my tiger oscer whom I call oscar had started to behaving strangly. He had started to in my opinon standing on his head a lot. I would poak him with the net and he would move in the correct way and start swimming around the tank. The morning i got up and he was in the same position as before so I tapped him with the net again and he sarted to swimming arouns again. He stays in this upside down state until he is bothered. My question is , Is my fish dying or what is wrong with him?