If you live with your condition your whole life and only you can perceive it, there's no way to know that it's not normal.
Take colour blindness for example, my friend had no idea at all he was colour blind until I had him take a test for fun and he read the numbers completely different then normal. I then asked him what he thought the colour of his pants was. He said brown, but in reality they were purple

. Living your whole life with mismatched clothes, all because he couldn't tell what he was wearing.
He was lactose intolerant too, he just thought his bad gas was normal

.