No, they are not the same. They both will make you sleepy. However,
valium is for anxiety, solely. I'm sure there are some docs out there that prescribe it to help people sleep.
Soma's are muscle relaxers, and they will make your muscles relax and make you sleepy. If I were you, I would not take them at the same time until you are at home and see how you are going to react to them. You could just not take the valium unless you are feeling a panic attack coming on. Then you won't have to worry about being too sleepy.