For the pacu attacking the koi, I noticed at work when customers bring in pacus who are fed mostly feeders those pacu normally fight with the plecos and other herbivores in the aquariums. Pacus who are fed veggies tend to be more gentle. I think the pacu saw the koi as a competitor who was taking all of it's potential vegetable based foods such as koi flakes or pellets.
As for the pacu freaking out right now, I would just remove all decorations, shut off the lights in the room and tank and hope the pacu falls asleep before it hurts itself any more.