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Interesting. It has been established that people with ehlers danlos syndrome and fibromyalgia often have increased perception to noise and light, and both these are associated with fatigue. It would make sense that you are more fatigued for the second show of the day so maybe experiment with getting in a half hour nap between shows if possible? See if that has any effect?

Dehydration, emotional or physical stress, and poor sleep hygiene can all result in reduced blood flow to the broca region of the brain, which is crucial for speech and audio processing. This is most frequently identified due to speech issues like gibberish or slurring (i.e., some of the more extreme/exotic symptoms of ptsd), but it also can manifest as hearing issues. Google up Broca's Aphasia for more information on that. Due to the fleeting and temporary nature in which most experiences of altered hearing occur in otherwise healthy people, this connection usually only registers with people who have another persistent issue which is the underlying cause. You, a little bit outside of the norm with a trained ear and all, seem to have cued in on this. Right idea, right observation.

Try to relax, drink water, maybe try resting the day before a show. Avoid the salty foods, maybe do some pushups to keep your heart-rate going between shows. The best solution is all going to depend on how you're built.

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Is there any indication that the blood flow / operation of the ear / auditory nerve itself is affected by tiredness?

Thats really interesting. I wonder if this is why after a night shift I struggle to speak and music sounds a bit distorted.

Ever talk to someone who hasn't had their morning coffee?

This is a well-known phenomenon among people with autism and ADHD, a population that significantly overlaps with the Ehlers-Danlos and fibromyalgia crowd mentioned in the post by u/Onikenbai, but it affects all humans to varying degrees of severity.

The best way I've heard it explained, that jives with my own lived experience as well, is that our brains are highly sophisticated filters that tune out the majority of our sensory input.

Think about focusing on a single sound in a noisy room, or identifying one flavor in a complex dish. Now imagine the opposite where you're simultaneously focusing on EVERY sound in a noisy room, AND the food you're tasting, while feeling every square inch of cloth that's touching your skin, the weight of your body on your joints and muscles, every scent in the room, the air currents pushing on every exposed hair....

You would be in a full-bore sensory meltdown and someone would probably find you rocking back and forth in the fetal position on the floor.

That's what our brains try to prevent every second of our lives, and it is a very taxing, resource intensive process. When we're tired, our brains are trying to do the same job with fewer resources, so the filter isn't as effective. Sleep deprivation, low blood sugar, dehydration, and simple end-of-the-day fatigue all stress your brain's ability to filter out unnecessary information. The result is that everything is a little louder, a little brighter, a little more intrusive than it would have been earlier in the day.

A fun example of this that could happen to anyone are the shingles scars on my left shoulder and chest. They itch constantly due to damage in the spinal nerve branch that feeds that part of my body. There's nothing wrong with the skin, but it always itches because of the damage to the nerves.

I can't feel it right now because my brain has gotten used to it and filters out the sensation, like how you can't smell your own house unless you leave it for a while. If I miss a night of sleep though, those scars itch incessantly and there's nothing I can do about it except getting some sleep to recharge my brain.

The only other thing I can think of is if there's more background noise from outside the theatre earlier in the day that raises the noise floor and makes the sound system sound quieter. I imagine you probably have pretty effective sound insulation in a professional theatre though.

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As someone with relatively recent ASD and ADHD diagnoses, is this why sometimes music can sound slightly too fast? (Same effect whatever device it's playing on, very familiar tracks)

It's kind of intriguing figuring out if some things about me are due to either/both of those or 'regular' neurotypical preferences - I actually just had a discussion about sensory input and how much we tune out with my psychologist the other day. Brains are fascinating.

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