hello and welcome to NT.
a dx of MS can be frightening. what helped me was to read about and get educated. the knowledge helped me feel in control and made it easier to make decisions (like about meds).

i was initially dx'd without an LP. on neuro exam and mri alone. shortly after that my neuro wanted an LP and i agreed. i had mine at the hospital under something called floroscopy. it tells the dr where the needle is.

you've gotten all good advice. staying hydrated and laying flat is important.
mine went well. my pain was minimal and i didn't have any adverse side effects. i did have 2 O-bands which clinch the dx of MS.

good luck. keep us posted.