I'm so sorry you failed your first test but it's perfectly understandable given the situation. Good for you that you've rescheduled. I have test anxiety too. When I first started studying the saunder's book for the nclex, I had panic attacks and couldn't think. I felt so overwhelmed and didn't know how best to focus my energy.
What I ended up doing was the Kaplan online course. It was really pricey, about $400, but it saved me. I wanted to throw up when I typed in my credit card number, but I decided to look at it as an investment. And besides, it costs a lot more to have to wait another 90 days to test. But everyone is different. I have a lot of friends that studied saunder's and they were really happy with it, and they passed too.
The kaplan online course worked for me because I was able to study at home and had a laid out plan of how to study. Like you, I have a bad back, so I laid on my floor at home and listened to the lectures everyday. The structure allowed me to stay calm. I suppose it was handholding, but I was so anxious I needed it. I listened to the lectures for 4 weeks, and during the last week I did 100-150 of the practice questions a day.
When I took the real test, it felt like just more of the same. I knew what to expect and felt confident. I passed in 75.
But this is just what worked for me. Everyone has given you great advice on what worked for them too. Good luck! I wish you the best.