I'd be asking WHY they are doing a LP (Specifically what are looking for) ive had two (both 20 yrs ago) I only had a headache with one of them. You don't always get a subdural headache afterwards. Last time I looked it up the complication rate of the headache was 10-15% not everyone has the oligoclonal band patterns specific to MS in the fluid. The way it was explained to me in 2001 was MS is "diagnosed by exclusion" i.e. they exclude a lot of other disease states with various tests and if it's none of them it must be MS. IIRC the LP just checks for the banding in your CSF, meningitis, spinal cord tumor transverse myleitis and neurosyphilis
The headache, if you get one, is treated with some procedure called an "epidural blood patch"

I see this question was 5 yrs ago. I'll give you my experience on car anyone is afraid or anxious about it. I've had 2. The first occasion I did exactly as I was advised (not generally something I'm good at tbh) in terms of getting the right position. I think the idea is to stretch the spine so that the needle can pop through more easily...
I felt no pain at all. I felt a sensation from the needle at some points I think. But honestly no pain. I like to ask the question, 'Why' almost all the time so I can understand things more easily... Afterwards I drank water and lay flat on the bed for a few hours. In fact I slept but I was in hospital at the time.
Whilst I was having the Lumbar Puncture, the doctor asked me, 'had I fallen asleep'. To which I replied, ' no I've done as you asked and I'm staying as relaxed as possible but please crack on and hurry up'.
The second time was pretty much the same. No pain either time.
I hope this helps at least one person 😊🤗

Drink water lots of water, deep breathing and think about the beach. When I had one it was scary but fine. hope it goes ok.

Mine was quick and easy. No pain at all with procedure. The after headache was a little rough. I had no bands, but still have MS. So the whole thing seemed to be a waste.