For Anna Sumner, sleep was like a drug. In 2007, Sumner -- then 32 -- had already battled chronic drowsiness for nearly a decade. What had manifested as bouts of sleepiness beginning in 1998 had gradually worsened over the years. "I would awaken at 5 o'clock, and be unsure if it was 5 a.m., 5 p.m., or 5 a.m. the following day," Sumner said.

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