Amnesia

Amnesia is a mental condition in which the person temporarily or permanently loses their memory, either in part or in whole. People suffering from amnesia may or may not be fully functional in other aspects of daily living. Usually therapy is required to help the person remember things about their life that have been blocked out by their current mental state. In fiction, usually comedic, a blow to the head can either cause a person to be amnesiac or can restore an amnesiac person to the original mental state.

Mainstream Smurfs Media
In the cartoon show episode "A Mere Truffle", Tracker suffered with amnesia when he led his fellow Smurfs out into the forest to learn how to hunt for truffles on their own.

Empath: The Luckiest Smurf stories
In the EMPATH: The Luckiest Smurf story "Empath The Bandit Smurf", Empath suffered with amnesia when he was sparring with Century over the River Smurf, causing him to form an alternate personality that became the Bandit Smurf when two humans, Stanley and Simon, captured him and forced him to work as a thief in order to pay off a debt to the evil Vincent Devereaux.