If its done under xray guidance, then risks of paralysis I would think would be dramatically reduced. If you can't lie flat for the required length of time, then you could end up feeling incredibly ill with massive headache for days (and you wouldn't want to be doing any school stuff anyway) - though some folk get up and about and it doesn't affect them, and others who do lie flat still get the headache (like me). Yes, the procedure does carry significant risks - even when it goes ahead absolutely without problems. If they have to prod about to find the right place for the needle to go in you can end up incredibly sore as well.
From my reading, I really don't see what having a lumbar puncture adds to information for neurologists in a whole lot of cases, and I'd really be strongly asking "what would you be doing differently if I do have this AND if it does show up anything", because it may not be significant. Also ask what other testing would show up useful information (even things like repeated MRIs might be better).
Personally, having been forced into having one, when I now believe it wasn't really necessary, I would only have it done if I really believed it was absolutely essential and there was nothing else at all that could give the neurologist information. If its MS they are looking for, then it really isn't even part of essential diagnostic criteria, and a higher resolution MRI (3T or 7T scanner) would give them better info than a lumbar puncture. If you have been advised not by other doctors, then I'd definitely go by their assessment.
Go with your gut feeling on this. Ask them what alternative investigations there are.
