about the LP, what it can tell you related to MS is whether you have a chronic infection in your central nervous system, indicated by comparing o-bands in the cerebrospinal fluid, compared to normal serum in the rest of you. some ppl with "MS" don't have o-bands, so it's kinda 'meh' as far as i'm concerned.
here's a bunch of stuff about the test and what it can be looking for in general:
if you do get the lumbar puncture, show whoever's going to do it this site:
i think hopefully this stuff is pretty much common knowledge http://www.pulmonaryreviews.com/dec00/pr_dec00_puncturehead.html
, but maybe i happened to be one of the ppl that are not helped by even the most careful angle of insertion. i only found all this out after the fact and never asked my neuro how he'd done my LP. but if it comes up for you, why not be sure it's all known, when someone's about to stick the needle into your own spinal cord!!
they might tell you to stay lying down for a bit after, say, 30 min, but if you get the post-LP headache anyway, in my case it meant if i wanted to avoid going back for the blood patch on the puncture (after the crushing headache had gone on for days), i had to stop trying to function normally and go lie down for three days to give the wound a break from the pressure involved in being upright. it worked, i did not need the blood patch in the end.