I saw a video once about a recuse worker who called it the "Triangle of Life."
Basically, he said to lay next to, not under, a study object, like your bed if awakened at night. The reason made sense because roofs fall and objects fall on the sturdy objects creating small pockets of open air -- especially in an office building or home.
In Tennessee, we have tornados. If it hits you directly, put your head between your legs and kiss your arse good bye. If close to you, you have a chance if you can get to a place and are lucky enough to be in one of those Triangles of Life.
John