A Memory Bug is what happens when someone's memory is remixed to make them remember that they died. It's unclear what will happen if a memory bug is let to reside in someone's mind. The game just suggests that it could create some kind of confusion to the host because one supposedly can not remember that they died.
There is also the possibility that it could kill the host as when Nilin remixed Charles Cartier-Wells memory of remixing hers to make her remember that she died in the accident that injured her mother, it caused her to die the memory, though this could have been due to Charles using a prototype hunt glove, or because it was how the mind of Charles assumed the consequences of a memory bug to be, as he had never actually witnessed such an event.