I don't think Mufasa suffered. It probably made him mad that his brother killed him, and you can bet he worried about Simba! But as he says in the beginning, life is a circle. Everything gives its life so that others can live. I like to think it is Scar who really suffers here, Scar wants to be King but when he does become King it is hollow. Scar never gets what he wants and despite all the painstaking effort, lies and leading a pack of hyenas he still cannot find happiness. Mufasa lived a happy life, though a little short, it was Scar who truly suffers and is worthy of your pity not Mufasa. I could write a very interesting
term paper about the meaning of this scene.