For the record,  not all synesthetes experience anxiety, distaste, pain,  nausea,  or vomiting from the pain of it.  There are all different types of synesthesia and plenty of people with color-music synesthesia will find certain colors in music ugly the same as in physical color theory,  but it doesn't cause them any sort of physical pain.  For others it can when it's strong enough a reaction.....  I'm of the sort that it can cause incredibly intense nerve pain to certain timbres when they vary offkey - and that includes every part of a twang that is offkey....

But not all synesthetes experience pain from dissonance.  It's most common in the forms of color-music synesthesia,  but even among color-music synesthetes there are plenty who don't ever experience pain or nausea from it.... I'm just one of the ones who can experience excruciating pain in response to certain timbres when those timbres deviate from a true note and turn pitchy....

Weirdly,  I can also have a visceral nausea reaction to voices and accents even when I don't experience most speaking voices as colorful. (three exceptions I know of: Trinidadian accents,  Irish accents, and Senegalese French accents have color to their timbre - but these are all very musical accents where the lilt in them makes them seem almost sung.)

I also experience souls/energies/auras as color,  and there are some that when they get sick in their soul will make me nauseous or cause me to throw up if I have to be around them...  I've never met a Trump supporter or genuine believing Evangelical type Christian who didn't make me violently nauseous - even if they try to keep their bigotry closeted because it isn't "acceptable" to their peers.  I actually always get sick to my stomach and so nauseous I can't eat around them.  (and that happens in the north as well as the south,  lol) Typically,  a visceral nausea reaction toward a person is due to something sick or twisted in their soul....  And yes,  this does tend to make me lose my appetite completely in crowded places and many big cities (but also small towns)  where sick/corrupted souls congregate cause me to throw up immediately upon my arrival.

Usually nausea for me is about smells,  pain, migraines,  exposure to chemicals/pollutants, or something I ate that my body is rejecting. But the pain to my synesthesia of certain vocalists can do it,  as can uncolored voices/specific accents,  as can souls that are very sick inside....

Also. Weirdly enough,  I've never had any physical instrument that's out of tune make ma nauseous. Painfully out of tune to make me wince at the pain,  yeah,  but a physical instrument has never made me nauseous no matter how painfully out of tune in the way that a pitchy vocalist will even when they're so close to true that a cheap tuner wouldn't catch that they're offkey....  Also,  there are some vocalists who can be quite a bit off a true note and not cause me pain or nausea even though they're flat or sharp. There are also certain voices (as well as specific instruments like piano,  acoustic guitar, harp,  violin,  and cello) that will actually DECREASE my nausea and can help relieve my physical pain - which is why I turn to them and put them on repeat when I have bad migraines.

So the nausea inducing when vocalists are offkey or even the slightest bit pitchy might not be due to the notes themselves,  but something in their energy that is getting melded into their timbre  is also dissonant or a soul corruption that makes even the slightest bit wavering from true cause me pain it wouldn't if their soul was healthy...  I don't know that for certain,  but it's possible....it would make sense of a quirk that's always confused me where certain people,  their timbres/pitchiness only bothers me during some portions of their recordings/live shows but not earlier or later....

My weak stomach and my canary-like sickliness from pollutants/chemicals is enough to make ye believe in changelings from the fairfolk,  non?

You get used to it the longer and better you come to know me,  lol.