"Pay no attention to that man behind the curtain, or these innumerable press clippings falling out of my back pocket. I am OZ, I have spoken."
While not completely fitting the description of a freudian slip (it has to occur while the subject is conscious and awake,) your dream does speak of a stronger attachment than you would like to admit. And your inability to reconcile and/or accept that attachment is partly what caused the dream.
Lets say you have a crush on person A. Yet you spend every waking moment telling yourself, and anyone who will listen to you, that you definitely do not like person A. It is therefore likely that you will dream of person A being 'very sick' and about to die, at which point in the dream all your protestations fall apart and you FINALLY admit how much you do feel towards person A. If we try and tell our subconscious minds we don't like something, if we try to play Chicken with it, it will call our bluff.
Now, strong, intense, movie-star crushes and infatuations are perfectly normal and healthy. They actually are simulations, people we can safely develop feelings for and learn how to deal with those feelings before we actually have them towards someone not so far away. Gymnasts practice long hours at the gym before they ever try to perform in public. Same difference. Also, movie-star crushes are like song lists: who and what we like gives us a clue as to who we will be compatible with. People who like opera don't hang out at death-metal clubs, for the most part. Thus, your attachment to Heath Ledger is akin to you being attached to Lady Gaga. That also means that when you are ready for a relationship, guess who better be on your significant other's favorite list, at least a few songs (preferable the same ones you like.)
We fight to hold onto ourselves, as it should be. And we fight against anyone, including ourselves, who attempt to take that away from us. Heath Ledger is not going anywhere you don't want him to go.