You were killed. However, your body returns to life with two resident souls yours and that of an ancient, alien being. The other spirit awakened for a purpose, one that it keeps secret from your mind. There are occasional fights for control of your body.
Approaching adulthood you experience wanderlust and decide to travel, roll 1d6 to detirmine years spent travelling and think about where your character might have gone. (work with your DM to determine details)