K.L.
Stick to it. The EXACT same thing happened to one of my twins when he got sick at about two years of age. The little guy who was once a wonderful sleeper started to wake up because he had a fever and felt miserable. However, it took me a while to realize that he was feeling better but was now spoiled - he knew I'd come in to make it all better :) It was really tough for a couple of weeks, but I knew that crying it out was the way to go because he had previously been a good sleeper and there wasn't anything else wrong with him. By the way, his brother became an excellent sleeper through this debacle - I left him in the same room, so nothing wakes him still . . .