From press releases:

Antena 3 Yamaha d’Antin MotoGP rider Alex Criville held a press conference at Valencia, Spain Saturday, the site of ongoing IRTA team testing, to announce that he is taking a medical leave of absence from his career as a racer to have a disturbing medical condition evaluated.
“I have been forced to take a break from my sporting career due to physical problems” said the 31-year-old Spaniard. “Since 1999, I have had a condition whereby I temporarily lose consciousness from time to time. It is not serious, but after consulting the best specialists in the field I was advised to stop riding for a while, to take the time to relax and undergo the necessary tests.”
While Criville plans to have further medical examinations and tests, Team Manager Luis d’Antin confirmed that he would be looking for a rider to fill-in until Criville’s return to the MotoGP series. Criville’s teammate Norick Abe continued testing at Valencia, making the most laps of any rider at the Ricardo Tormo circuit Saturday with 51 laps and a best time of 1:35.908, making him fifth-fastest.