For me this has happen once recently. Here what happened, I have a very sever case of restless leg syndrome (my legs will kick even when I am asleep). When I sleep I have many times been "ejected" from bed because my legs have kicked so hard when I been asleep, a few times I have banged my head on the night stand. Well the other day I go over to amazon.com to buy a new plastic mattress cover, and they suggest that people have gotten the one I was buy has also bought a bed rail (you know the ones they put on normal beds for toddlers just starting out sleeping in a real bed) I figure what the heck I will try it to see if it helps, well the last few nights, I have not fallen out of bed because of my legs kicking (I have been woken up as I hit the bed rails, but that better then hitting my head on the night stand.)
And this because as a DL I need a new mattress protector encase my diaper leaked at night.