The deep / Nick Cutter.

"A strange plague called the 'Gets is decimating humanity on a global scale. It causes people to forget--small things at first, like where they left their keys...then the not-so-small things like how to drive, or the letters of the alphabet. Then their bodies forget how to function involuntarily...and there is no cure. But now, far below the surface of the Pacific Ocean, deep in the Marianas Trench, an heretofore unknown substance hailed as "ambrosia" has been discovered--a universal healer, from initial reports. It may just be the key to a universal cure. In order to study this phenomenon, a special research lab, the Trieste, has been built eight miles under the sea's surface. But now the station is incommunicado, and it's up to a brave few to descend through the lightless fathoms in hopes of unraveling the mysteries lurking at those crushing depths..."-- Provided by publisher.