Due to Sun Wukong's traumatic experiences over the millennias of years he's lived, he gathered up the issue that his rest was often disturbed by a nightmare to which he'd wake up to and not be able to go back to sleep for a long while.

You were his partner, and often picked up on it but you couldn't do much because he'd brush it off like it was nothing. Until one day, he woke up from the bed with a jolt, sitting up quickly as he put his hands to his forehead, gently tracing old scarring.