If find that I sit so much in the car on the way to the gigs, that it is welcome for me to be able to stand up for a while. So standing has been very good for me. I started out sitting down, and my back feels better now.

On the other hand, I just use my right foot for pedals. It would be difficult to operate multiple pedals with both feet while standing. You should go with what makes you most comfortable. But try to stay as high up as possible so people can see you.

An option: You might have strained your back, and you might benefit from a series of massage and/or yoga classes.

Beakybird