i was about feed and the tank lights were off i heard a loud thump and i turned on tank lights my arowana 8-10 silver was so lifeless and i thought for sure he was a goner just floating and hope just not there , i watched for 5 minutes and went kitchen he was back at the top and looking about 85 percent normal , time passed back looking 100 percent and eating like nothing ever happened , i guess when i approached him with lights off he got scared and hit tank , he knocked him silly glad he is better , this ever happen to anyone 

This is what happens when you have too many tanks and have no room to keep a washer/dyer.