The astronaut who prompted NASA's first medical evacuation earlier this year said Friday that doctors still don't know why he suddenly fell sick at the International Space Station.

Four-time space flier Mike Fincke said he was eating dinner on Jan. 7 after prepping for a spacewalk the next day when it happened. He couldn't talk and remembers no pain, but his anxious crewmates jumped into action after seeing him in distress and requested help from flight surgeons on the ground.

"It was completely out of the blue. It was just amazingly quick," he said in an interview with The Associated Press from Houston's Johnson Space Center.

Fincke, 59, a retired Air Force colonel, said the episode lasted roughly 20 minutes and he felt fine afterward. He said he still does. He never experienced anything like that before or since.

Doctors have ruled out a heart attack and Fincke said he wasn't choking, but everything else is still on the table and could be related to his 549 days of weightlessness. He was 5 ½ months into his latest space station stay when the problem struck like "a very, very fast lightning bolt."