An overload spell, also known as sensory overload, was a headache common amongst Chiss sky-walkers in the Chiss Ascendancy. If the sky-walker was worked too hard or navigated into a multi-star star system, it would take a toll onto the individual and cause a spell to start when awakening from Third Sight. Sky-walker Che'ri suffered from an overload spell when entering a quadruple star system aboard the Springhawk in 19 BBY.
Symptoms included a severe headache alongside sparkle-vision and vertigo which hindered the sky-walker's readiness for navigating.
Overload spells were first seen in Thrawn Ascendancy: Chaos Rising by Timothy Zahn which released on September 1, 2020.