I was hesitant to clean the piranha tank I had but it had full gorwn red bellies. Thhey never jumped out, but would always moved round and bump things at night. IMO, they are not agressive fish at all. They are very shy and act agressively only by fear/hunger. It seems that they think everyone wants to kill them and the only way to survive is to kill them first
I would move your tank not because of them jumping out, but because I wouldn't want to spill any water on my bed. Water is bound to get out of the tank by accident during a water change or from the fish jumping.
Just for your reference, if a piranaha would jump out of the tank, its not just going to sit there. Expect it to flip around with every muscle in its body. You might find it 10 or more feet from the tank if it does jump out.