I have experienced this several times and almost never have a headache. I definitely can't read what's beyond/obscured by the scotoma. The first time it happened was during a test in high school and the splotch grew until I was forced to read the questions in my peripheral.
I have an anecdote that corroborates your observation that cognitive experiences are more complicated then assumed: I was once very, very sleep deprived. I became aware that my body was reacting to something, as if there was a jump scare in a movie, I unconsciously flinched and pulled away from something without knowing why, and then a perceptual moment later, I heard a loud noise caused by something falling to the floor.
I have an anecdote that corroborates your observation that cognitive experiences are more complicated then assumed: I was once very, very sleep deprived. I became aware that my body was reacting to something, as if there was a jump scare in a movie, I unconsciously flinched and pulled away from something without knowing why, and then a perceptual moment later, I heard a loud noise caused by something falling to the floor.