So, basically we could all be on acid 24/7 and not notice, as long as everyone else was tripping. That's gotta make you wonder what existence is all about.
But we could be vitamin deficient, in various columns.
We could be having low-level allergic reactions, caused by environmental factors we're too busy (or dumb?, sometimes?) to correlate right away.
We could have an infection, or a cancer, hollowing out a part of our body, and not quite know what that feels like.
Tons of things like that.