Ken - I wonder why bunks are not certified for take off and landing.
IIRC seats are required to withstand 9 Gs in forward deceleration, 2 Gs upward, 1.5 Gs sideward and 4.5 Gs downward.
I would have the forces in a crash would be much more palatable for a prone body, than an upright one; but am no expert.
A prone body strapped into a bed would slide out from under the seat belt.
Even if one could properly restrain a body in the bed, there are no escape paths in the bunk area(s), so emergency evac would be problematic at best.
And no food or drink is allowed in the crew bunk areas so I'm assuming that would be true of passenger bunks as well.