Why it doesn't feel like height after takeoff
Without a visual anchor (a tree line, a roof) your body can't read distance to the ground. After takeoff most passengers report no height-fear at all — only the sensation of motion. The cabin is genuinely a sealed room; the height is abstract.
What to do about the window
Looking down from cruise altitude is a choice. Aisle seats remove the visual trigger entirely. Some flyers prefer a window seat with the shade pulled — privacy plus zero ground reference.
Why pilots trust the air at altitude
At 35,000 feet the aircraft is in its design sweet spot. The air is thinner, smoother, and more predictable than at lower altitudes. Pilots actively want to be up there — a high cruise altitude is the safest, calmest portion of every flight.