The Masters of Sleep — L. Ron Hubbard

Under the Curse of Eternal Wakefulness, Jan Palmer had never slept for years, but had been  transferring from the Land of Awake where he was Jan Palmer, harassed President of Bering Steamship Corporation in Seattle, Washington; into the Land of Sleep where he was Tiger , a brave sailor in the land of the Jinn, where Ifrits were masters and the sleep-souls of humans were the slaves. 

But if the Jinn world was pure make-believe, then why does Jan Palmer find himself suddenly thrown into it with gruesome reality, when he came to find the Two-World Diamond in his pocket?

Having no recollection of his dual nature, Jan was facing insanity from a crazy psychiatrist, Dr. Dyhard, who's bound to drill his brains any moment; and death for Tiger being chased by Jinn rulers -- Zongri and Arif-Emir, and the fleet admiral, Tombo -- with fleets of warships, for stealing the Two-World Diamond.

Survival  now was beyond Jan's finding solace with his wife Alice who at the same time was Wanna, Tiger's temple dancing girl; nor expertise of Tiger's fully able-bodied crew of four:  a murderer, a professional strong-man, an ex-pick-pocket, and a navigation-expert child. Nonetheless, both Jan and Tiger knew that their slim chance of survival lies in whatever powers the mysterious stone might have. And they better know it fast before time runs out!