There were several good posts within this discussion that talks about how to do it safely. I think most of us agree that you will seldom sleep as good as you would stretched out in a bed or tent, but it's safe as long as you use good common sense. If you have any questions of how to do it safely, ask again. But I think you can find the answers with a thorough read-through.

Of course, we can't guarantee that nothing will happen but it's about as safe as anything else when done with common-sense.

Hope that helps a bit.