You made your bed, now lie on it

Physics Central...

It all comes down to pressure, or the force per unit area. When lying on a bed of nails, our body exerts a force equal to our weight. Although that's a significant amount of force, all of that force is distributed across the hundreds of closely-spaced nails on the bed.

When there's plenty of nails, the pressure any single nail exerts on the skin is quite small, resulting in no pain and no cuts. Resting an entire body on a single nail, however, would be a different story.
 
I still wouldn't do it.