An astronaut who nearly drowned this week when his helmet filled with water has revealed terrifying details of the experience.

Luca Parmitano, 36, almost drowned during a July 16 spacewalk. The Italian astronaut chronicled the experience on his blog.

Before it happened, Parmitano said, he felt like "

"I'm not tired -- quite the reverse! I feel fully charged, as if electricity and not blood were running through my veins. I just want to make sure I experience and remember everything," he wrote.

However, all that changed quickly. After Parmitano and NASA astronaut Chris Cassidy got out the door of the space station and locked safety cables into place, they went off on separate routes to the same part of the exterior of the International Space Station.

Parmitano had a more direct route and finished his first tasks very quickly-in fact, he over40 minutes ahead of schedule.

Then things went wrong. Very wrong.

"At this exact moment, just as I'm thinking about how to uncoil the cable neatly ... I 'feel' that something is wrong. The unexpected sensation of water at the back of my neck surprises me -- and I'm in a place where I'd rather not be surprised."

As it turns out, the liquid was from his spacesuit backpack, NASA now knows. Parmitano alerted mission control, and Cassidy came over to attempt to figure out where the water is coming from. It wasn't sweat or  a drinking water valve leak....so what was it?

Mission control told him to go back inside the airlock. Water was running inside his helmet, obscuring his vision. He had to go upside down to release the safety cable.

"Two things happen: the Sun sets, and my ability to see -- already compromised by the water - completely vanishes, making my eyes useless; but worse than that, the water covers my nose -- a really awful sensation that I make worse by my vain attempts to move the water by shaking my head. ... I can't even be sure that the next time I breathe I will fill my lungs with air and not liquid. To make matters worse, I realise [sic] that I can't even understand which direction I should head in to get back to the airlock."

He felt his way back in frantically, fiding handles that lead to the airlock and scrambling inside. They started the repressurization process.

However, as they repressurized, Parmitano lost audio contact. Water was filling his ears, and he felt he was drowning during the whole process, which takes several minutes.

Still, he figured fainting would be better than drowning.

"Finally, with an unexpected wave of relief," the repressurization process was over, and the other crew members aboard the Space Station rushed in to remove his helmet.

For now, NASA has suspended all spacewalks as it investigates why equipment malfunctioned.

He closed his blog post by saying, thoughtfully,

"Space is a harsh, inhospitable frontier and we are explorers, not colonisers. The skills of our engineers and the technology surrounding us make things appear simple when they are not, and perhaps we forget this sometimes.

"Better not to forget."