No, Michael Jackson did not sleep in a hyperbaric oxygen chamber.
The rumor: Michael Jackson religiously slept inside a hyperbaric chamber in the belief that it would grant him unnaturally long life. This rumor started in 1986 when the National Enquirer (AKA the Least Reliable News Source Ever) published a photograph of Jackson laying inside an actual hyperbaric chamber.
The reality: While the photo IS real, this was a piece of medical equipment inside the Brotman Medical Center’s Michael Jackson Burn Unit, where he was treated for severe scalp burns in 1984. Jackson donated vast sums of money to the Burn Center, making the purchase of this piece of equipment possible. The photo was taken when he crawled inside, being a perpetual joker, and pretended to be asleep.
The end. The truth doesn’t make for very good tabloid fodder, does it?