Light wave sickness

Light wave sickness was a sickness fatal to the Daleks but not fatal to Spiridons. The Daleks conquered Spiridon, hoping to discover the secret of the Spiridons' invisibility and reproduce it for their own use on an army kept in suspended animation. Only one Dalek used it, but it died from light wave sickness. The Dalek was examined by the Third Doctor. The invisible Dalek was discovered by the Third Doctor and a group of Thals. With each invisibility experiment, the Daleks became more proficient with becoming invisibility though it was enough to satisfy the Dalek Supreme when he arrived on Spiridon to release the army when it was time to begin the invasion of the galaxy. (TV: Planet of the Daleks ^[+]Loading...["Planet of the Daleks (TV story)"])

After being the Daleks' prisoner for many years to try and restore the Spiridons' invisibility so that the Daleks could duplicate the process, the Seventh Doctor released a contagion that gave the Daleks the light wave sickness. This destroyed all the Daleks occupying the planet, while affecting the Doctor with the light-wave sickness until he returned to the TARDIS, the TARDIS's dimensional stability keeping his cells immobilised until they overcame his cellular paralysis. (AUDIO: Return of the Daleks ^[+]Loading...["Return of the Daleks (audio story)"])