I don't recall it ever being a problem when I was on stage. There was usually time off stage where a bathroom break could be worked in, if needed. Not always though, but as others have said, "Your mind is on other things."
I do remember the the one that freaked me out the most was when I played the Tinman in The Wizard of Oz. Once I was wired into that costume, there was no going back. I usually waited until the Munchkinland scene was well under way, before I was helped into it. The barrel part around the chest didn't allow for my legs to bend beyond a certain point (just like in the movie), so there was NO sitting down. So, not only couldn't I "go" but I couldn't even sit during intermission (which was my only time off stage, once I made my entrance).
I don't remember ever having to "go," though. I would get out on the stage and roast in my costume, under those hot lights. I usually lost around 8 pounds every performance. Just water weight, but I would have to drink gallons of water AFTER every show to make up for it. It was like a 2 hour sauna. But I don't think there was any water left inside me to "relieve" while the show was on, anyway.
"Jaws is the Citizen Kane of movies."
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