I"Ve had three experiences with a lumbar puncture. The first as a young boy when They couldn't get the needle in and the operator ended standing on the operating table, to drive the needle home. The second was completely uneventful and painless. The last time the puncture leaked and I had a three day headache. The leak was patched by injecting some of my blood back into the leak so that the blood could scab over and shut the leak..and that provided immediate relief.
On a scale 1 to 10, I'd rate the experience an 8, 10 being the worst. Good luck.