Whats a lumbar puncture like and why should someone lie on his or her back afterwards?

LP: A lumbar puncture is a procedure in which a physician will insert a needle into the spinal canal to collect spinal fluid. After a hole is placed into the sac which contains the fluid, fluid can leak out which can result in headache or what is referred to as a spinal headache. Lying flat after the procedure reduces the likelihood of this happening which is why patients are told to lie flat after a lumbar puncture.