hi stapes, i'm totally new to this forum, too- and also have just been diagnosed, so i can really relate to how you must be feeling. i'm wondering, if you already have been diagnosed, why the lumbar puncture? in my case the lp was done in order to get additional information to secure my diagnosis, otherwise as far as i know a lumbar puncture result doesn't make any difference for your treatment.
but just in case you really need to have it done, i'll tell you about my experience:
to be on the safe side, i would definitely take a couple of days or even a week off work or any other obligations you may have, as it is possible that you get strong headaches (i've read a lot that most people don't get that at all, so don't worry too much, but just allow for the possibility).
the lumbar puncure itself is definitely not painful, you will lie down on a bed and curl up in a fetal position, then the doctor will disinfect your lower back and inject an anesthetic and then direct the lumbar puncture needle between two vertebrae in your lower spine. this is in a location where he can't possibly hit your spinal cord anymore (it ends above that location), but the sac around the spinal cord which contains the spinal fluid extends below that level, so it is safe to collect spinal fluid at that level).
so it is really safe to put the needle in there, you won't have to watch it either and you also have been anaesthesized there, so it's not going to be painful. you'll just have to lie there as still as you can and try to relax if possible, take your partner or a friend with you, that helps also.
what i didn't get but learned later is that the doctor can additionally use a fluoroscope to make it easier to find the right spot, ask about that!
afterwards, you will need to lie down for at least 45 minutes, some even have their patients overnight, but i was sent home after that. make sure you've got someone to drive you home and then immediately lie down and drink lots and lots of fluid- and you'll be fine. should you get the headaches ibuprofen worked well for me and they also lessen as soon as you lie down.
let me know if you've got any more questions!
all the very best and hope to meet here again!!