Spatial disorientation

The inability to correctly sense attitude, altitude, or airspeed when outside visual references are lost.

As taught in Controlling the Airplane by Reference to Instruments (Flight Instruments and Avionics) — a free lesson with cited FAA sources.

Inability to correctly sense the aircraft’s attitude, altitude, or motion.

As taught in When Your Senses Lie: Disorientation, Motion Sickness, Ears and Night Vision (Aeromedical Factors) — a free lesson with cited FAA sources.