That's what I automatically assumed when I saw the film. I imagine that it was probably a nightmare concerning his father's death, or perhaps simply his guilt (in his thinking that it was his fault).
I , when I was younger just thought it was a normal kiddy dream due to the light hearted-ness of the film.
*I'm looking to RP : *Young Justice *Dinosaurs *Nightmare before Christmas *Yu-Gi-Oh! Copy/paste this if you're proud to be an atheist too! Love you emily123!
He probably dreamt about a lot of bad things. Mufasa dying, Sarabi hating him for "killing" Mufasa, worrying if Scar would tell the others Simba was "responsible", Nala missing him, the Hyenas finding him, Timon and Pumbaa abandoning him. He's had it pretty rough for a Disney prince.