Hi, Jenny. I had my first spinal tap a week and a half ago. I barely felt the needle for the numbing (novocaine in mouth is MUCH worse in my opinion) and the tap itself was completely painless. My neurologist did it, she said your position when they do it is important. I guess I was very fortunate that I was on a comfortable hospital bed, they positioned me on my side, curled up sort of but keeping my shoulders squared. I stayed flat on my back for about 2 hours afterwards then drove home, no problem. I DID apparently make a mistake when I assumed I could just resume normal activities, in particular bending over to care for/play with my puppies. 24 hours later I did get "the headache", it lasted 4 days, until I stopped bending over and started squatting when I had to get something off the floor! My back was a little tender, not a big deal.
It sounds much worse than it actually is. I understand they used to be horrible, but it really isn't a big deal any longer. You will do just fine, stay calm, it makes a big difference!