Why valium over soma?

On Thursday June 23rd I had a cervical spine fusion surgery. Before my surgery I was taking 1 soma 350 on most nights to help with muscle spasms. On my release instructions from the hospital they said not to take the Soma any more. The nurse told me it was "not good to take". Being not very "with it" at the time I just said ok. The nurse told me to call on Monday for something else if I was still having the spasms. So today I called and they prescribed 5 mg valium. Isn't Valium more dangerous than Soma? Why would they make the change? I have also been taking percocet for the pain. Does it have something to do with that?