Would you feel comfortable sharing how you feel with the people you're going with? If it were my friend, I would rather her let us know and still come even if she just wanted to be still and quiet and take it all in. I wouldn't want them to feel like they needed to perform if they were feeling drained. Also if it gets too much during the show and you need a breather you could just say you're popping to the loo or to get a drink and have a time out. Ear plugs also really helped me, makes it feel much less intense!
Sending you a huge virtual hug
Also edit to add - there is no such thing as normal so try not to be too hard on yourself, I'm sure you're absolutely lovely the way that you are!