Fourth Doctor's regeneration

The Fourth Doctor underwent his regeneration into the Fifth Doctor after falling from the Pharos Project telescope. (TV: Logopolis) This was the fourth regeneration of the 12-regeneration life cycle beginning with the First Doctor. (TV: The Time of the Doctor)

As Doctor anticipated his death while dangling, his mind flashed memories of, a Dalek, the Nomad Cyber-Leader, the Captain, Davros, a Sontaran, a Zygon, and the Black Guardian.

After the fall, he saw Sarah Jane Smith, Harry Sullivan, the Brigadier, Leela, K9 and Romana's first and second incarnations. (TV: Logopolis)