Just an update:
The doctor wouldn't write me a letter to give to the builder without a full diagnosis in my condition. However, the sales rep called me and said to just send her an email stating that I wanted to cancel, and the reason for the cancellation. I asked her if she had some bites on the property, and she told me that she's got a lot of people ready to move on it once she gets a letter from me. I asked her about the earnest money, and she told me it wouldn't be a problem due to the popularity of that particular lot. They stand to make about an extra $50K now, so the $5k to me is a drop in the bucket I'm sure. Well, it looks like everything is working out fine. Thanks for the support!
S