The man had fallen asleep on the toilet in Manchester University's Sackville Street building in England.
When he woke up on February 15, he found he was locked in the building and called the police.
It is believed he was in the building the night before and passed out when he went into a cubicle.
Officers were sent to the scene to help him - but the man rang back before they arrived saying he had managed to get out and was now walking home.
"A police response was allocated to attend but he then called back to say he had got out and was going home. We have been making these calls public to encourage people to think before they dial 999," Pickford said.