Dreamland came out last year in hardcover. Though I wanted it immediately, I managed to wait for a paperback to turn up at Half Price Books.
I really like this book, but it isn't as long as it appears or should be. Sure it's 266 pages, but look at the typesetting—the space between lines is unusually large. The chapter about sleep apnea is informative but could be longer. I also expected to read more about REM sleep disorder, which Mike Birbiglia has written about (unscientifically).
Ultimately there are a lot of unanswered questions in sleep science. It is a fairly new area of study. REM (rapid eye movement) wasn't discovered until the 1950s, and the CPAP machine, now a common remedy for sleep apnea, wasn't devised until the late 1970s (using a vacuum cleaner motor!). All of this adds up to a short history with a lot of uncertainties, and that's probably why this book isn't longer.
Dreamland also cries out in need of an index—there are even twelve blank pages at the end of the book!