Which is worse: to have your head resting against a concrete floor and then be struck by a hammer (A), or to be standing upright and have your free head be struck by a hammer (B)?
Perhaps these diagrams will help you decide.
If you supposed that situation B was worse, you are correct. In fact, the brain is much more susceptible to injury of motion than it is to the application of forces while in a stationary position. Despite the fact that your head is basically being drilled into the concrete in situation A, the brain is more likely to be protected by the skull and less likely to impact the inside of the cranium. In situation B, the freely-moving head will stop more suddenly than will the brain, and the resulting impact of the brain upon the skull is likely to cause cerebral edema.
Ergo, vis-a-vis, concordantly, the next time someone attacks you with a blunt object, lie down. And pray.