That's right cockney, and something else you mentioned about the rest slamming down seems likely too, somebody dismissed your comment about that, but obviously a severe crash is going to create many tens of g's of force, possibly increasing the effective weight of the rest 40+x.
Imagine the if the armrest only weighed half a kilo. That's a potential of 20kgs+ of force which, if it hit you in the back (if your body happened to be moved laterally upon impact) it would smash into your spine. Just something else to consider, as cockney said. (I think the spine can absorb forces of about 20-25kgs before it gives way. (I watched on an anatomy programme).