The British actress was in Spain shooting her role as soprano Maria Callas in 1988 movie Onassis: The Richest Man in the World when she fell ill - and her treatment at a local medical centre took a turn for the worse.
Seymour believes that during the near-death experience, she floated out of her body and saw doctors administering treatment.
She tells Britain's Sunday Express,"I was filming in Madrid when I got a very bad cold. A doctor suggested a shot of antibiotics but unfortunately the nurse put a massive dose into a vein and I went into anaphylactic shock.
"Mercifully I was resuscitated but there was a period where I left my body and clearly saw this man screaming on the telephone and my naked body lying on the bed with syringes in my backside."