XP level saving

I currently have a "dream dimension" sort of thing where if a player sleeps, they are sent to it with an empty inventory, their real inventory is saved at their bed w/ chests, and after a certain amount of time, they are sent back to their bed. 
The problem is, I don't know how to approach saving XP levels, I originally thought about copying the data from the player into an xp orb, however XP orbs use absolute xp value, while it seems the player data only stores levels,
Any ideas?