“Experts said flying a Boeing 777 in such a way would be dangerous, stressing the airframe and possibly causing those on board to be air sick and suffer from spatial disorientation.”
Why is the airframe stressed? At a low altitude, the cabin is barely pressurized.
Air sick? Depends on turbulence and visibility. Air sickness is usually the eye and the inner ear trying to resolve perceived discrepancies, leading to nausea.
Spatial disorientation? Turn on the autopilot.
Look up maneuvering speed and turbulence and start learning about aviation.
I'm no expert, but it occurs to me that high speeds at lower altitudes probably cause more stress on the airframe due to the increased air density.
Combine that with being closer to the ground, the heat radiated back up would probably cause increased turbulence, though I admittedly don't know what the effect would be over the ocean.
Mark
-— Why is the airframe stressed? At a low altitude, the cabin is barely pressurized. -—
Force equals mass times acceleration. Rapid changes in altitude represent high acceleration. And planes are built with a low factor of safety.