Dog bites master bad,he has no issues(dog is healthy)keep it or end it?

He is a labrador,4 years old and so far everything was fine.He has 3 sons but i have neutered him a few years back,and vaccines and stuff like that.Yesterday he bit me...he was going for my face but i pulled my arm so no it s my arm.The dog was asleep but he had a mirror right in front of him,on the wall.He woke up for some reason,saw himself in the mirror i think and started to go ballistic and bit me,thank god it was the arm,but he was jumping for my face.I left him outside right now but why did the dog react to the mirror and started biting me?What should i do with Spike now?He is castrated and vaccinated,i took him to the vet after fixing my arm,and the vet gave him a clean health,but can t explain this behaviour.And i get bored watching Cesar and Dogs on NG...what should i do with the mutt and why did he react this way?