One of my beardies died today.

I noticed he/she wasn't eating the last couple of days. The beardie took one woodie last night but didn't seem well. The other 2 beardies didn't eat much today either but there bigger than this one - especially one in particular. Any ideas what could cause a beardie to stop eating and then suddenly die (eyes were still open)?
Also, one of my other beardies was walking with a limp yesterday as well. What could have happened all of a sudden?