Take breaks. It's easy to get sucked in to answering questions, etc on the breaks, but you deserve and NEED one too.
When you stop and are waiting because people are working (building a Light Cue, backstage needs to talk through a costume change, etc) make sure you know who you are waiting on and that THEY know who you are waiting on. Many a tech minute has been wasted and followed by the words "oh, were you waiting on me? I'm done"
Breathe.