Hi Vallerina, I had the same problem with my air expander. It was uncomfortable and hard - I was never really able to sleep well with it the whole time I had it. The advantage was being able to expand it myself...but I was certainly very glad when it was replaced!
I had to create a pyramid of pillows to enable me to sleep well at night because it was just so hard (I likened it to having a brick or a handbag sewn into my chest!) I also experienced the zapping nerve pain. It does however lessen over time...
Nikki