my oscar is about 6inches now and ive had him since he was a baby, about a month after i got him he started laying down it looked like after he ate, now he does it all the time, but when u walk up to the tank he pops right up and is normal again, my water perameters are withn norms and i do water changes reglarly, its a 100 gal tank. is this normal behavior, has anyone else encountered this