From "The Prisoner", part 1 of the series' penultimate episode,"Degree Absolute", in which No. 2(played by Leo McKern) engages in a psychological battle with No. 6(Patrick McGoohan), in which there can only be one winner.
The intensity of the episode, and of the performances given by McKern and McGoohan therein, resulted in the physical collapse of Mr. McKern on the episode's set at one point during its filming.
Be seeing you.