Rabbit died suddenly- has anyone experienced this?

[thevanguard6]

I've seen something like this before. In the case that I'm aware of, it was caused by pneumonia. As such, I keep rabbits away from drafts and I keep them dry at all times. Some are more sensitive than others. Some general info here:
http://www.blitter.com/~nebulous/otherworld/RabbitCareGuide.pdf