If someone has a headache, it is very serious to them. During the acceleration, a human body gets exposed to strong g forces for the duration of the acceleration.
Pilots and astronauts that are regularly exposed to these forces must have exceptional health and must actively work on maintaining thier body in tip top shape as some health issues may rule them out of their job.
Couple of links on the subject,
Nasa and
Encyclopaedia Brittanica
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Maybe in the future Tesla will need to put some appropriate health stickers on a dash, or pop up acknowledgement screen on the insane mode.