When I had my LP I only took in a 500ml bottle of full fat coke. That seemed to be enough to prevent a headache, that combined with lying down for an hour when I got home.
The doctor/ nurse who carried out the procedure didn’t think much of leaving me to remain lying after they took the needle out. I didn’t get a headache at all, but I did feel as though some pressure was relieved from my neck afterwards. I ahd walked out of the room about 10 mins after te LP and was in my car driving home.
All in all, it wasn’t to bad. When I arrived I had to sign a medical disclaimer and then jump up on the bed. I was then asked to pull my t shirt up a little to expose my lumbar region and then the nurse applied some sterile wipes.
The nurse gave me a local anasthetic then the doctor carried out the procedure. All I could feel was a bit of prodding in my lower back. No pain though just prodding. It seemed to take forever, but in reality only took about 40 minutes tops. I must have a fat back as they struggled to get the needle in.
I left the sticky plaster on for a few days and left the area well alone, just to be on the safe side.
Good luck with it.