As Carter hid in the cave, he heard "a sharp click as of the snapping of a steel wire" and then found himself gazing at his own body. Of course, you can gaze at your body too; just look in a mirror. Yet Carter knew this was not a reflection because the body on the ground was clothed, but his own body was naked: this Carter body and that Carter body were not the same body.
Carter next supposed he was a ghost, so he pinched himself and, feeling the pinch, he concluded he was not a ghost. Yet he could not bear to touch that other body, "for some unfathomable reason," he says. It's not unfathomable at all: Carter was experiencing the uncanny sensation of knowing that he was dead (he saw his lifeless body) and knowing that he was alive (he felt his living body).
A dream perhaps? Perhaps. He could have dreamed he saw his body, dreamed he pinched himself, dreamed the Martian adventures ... but no, this was no dream visit to Wonderland on some drowsy afternoon. When Carter returned, ten years had passed.
During his next Martian visit, Carter's corpse - confirmed as dead by the New York coroner - spent twelve years lying in a Virginia vault. Carter says that there in the New York snow, just as in the Arizona cave, "came the sharp click as of the sudden parting of a taut wire, and I stood naked and free beside the staring, lifeless thing that had so recently pulsed with the warm, red life-blood of John Carter."
This death was not the "real death," presumably because the corpse did not decay. Even so, if anything does await us after death, it is bound to be uncanny - and, speaking for myself, I would like for that death, real or otherwise, to give me a chance at interplanetary adventure, Carter-style.
Burroughs, Edgar Rice. A Princess of Mars. 1917.
Burroughs, Edgar Rice. The Gods of Mars. 1918.
Life and Death ambigram, at Ambigram Tattoo Designs.