Relax or brace is the question?
I heard once upon a time the Royal Navy did a study and considered doing away with seat belts and shoulder harnesses all together. They felt it would be a great savings in cost. They considered installing nice shiny chrome trailer hitch balls in the seat cushions and modifying their flight suits to allow for the pilots to accomodate for the modification.
It was supposed in a serious crash, clinching one's hind end would securely retain one in the seat.
If I see the ground arriving at near warp speed and know there is nothing I can do to prevent it from happening....getting my head down and curving my spine from the upright vertical position is the best I can do.
Rotor blades like to lop noggins in some types of helicopters and if you hit vertically with a straight spine you will risk some very serious damage as compared to being bent over.