CSF Flow Study

My insurance does not want to pay for the type of CSF Flow Study with the MRI so instead my Doctor scheduled the other kind with a lumbar puncture. Has anyone had one of these and is there anything that I should prepare myself for going into it? My doctor says that I will need someone to drive me home afterward because I will probably be in a lot of pain and have bad headaches. I'm just wondering if there is anything that I should know going into this test since this is the more invasive type of flow study I'm a little more nervous.