The Colonist inside a dream sequencer.
You may also be looking for Universal Migrator Part 1.
A dream sequencer is an immersive virtual reality device designed to allow the user to relive past events from a first person point of view. These events can be the memories of the user, the inherited genetic memory of the user's ancestors or previous physical incarnations of themselves through preincarnation.
The dream sequencer was presumably originally invented by the Forever. (Day Twenty: Confrontation, The Memory Remains). By the late 21st century humans possessed dream sequencing technology. This is likely one of the innovations brought about by the Forever accelerating their development during the 20th century. (Unnatural Selection).
In 2112 while using the dream sequencer the Colonist died while experiencing the events of a Universal Migrator. Somehow this combination of events allowed his consciousness to exist independently of his body after death and he became the new migrator. (The New Migrator, The Sixth Extinction: "Spirit on the Wind")