Okay, I can't figure out what I have done.

I am using the healing brush tool. All of a sudden the areas that I am healing are very highly pixelated...does that make sense? I don't know what I did..I didn't change anything, that I know of. Does anyone know what I did, and more importantly, how to fix it?

Check the options bar for this tool to be sure that you have not accidentally changed the brush's blend mode or switched the mode to "replace" or have the Pattern Option selected instead of the Sampled. Also check if your sampling option is set to the current layer or all layers. If nothing works, perhaps you can attached an image to this thread so folks can see the exact symptoms.
Regards, Murray

I have seen this before, it tends to happen if you use the brush in the same area a lot of times.
Also try making the brush eliptical, I don't know why it helps but it seems to work.

Hope this helps

Peter