Officers arrived at the scene shortly before 8am after receiving reports of an agitated man shouting and screaming in the middle of the city in western Norway.
Witnesses said they saw him try to assault his own reflection, newspaper Bergens Tidende reports.
“He was behaving strangely and had probably taken GHB or GBL,” said Ronny Lentføhr, the police officer who ordered the arrest.
The man did not injure anybody, police said.
“It may well be that he ends up in jail but first he’ll be taken to the emergency ward,” said Lentføhr.