Astronaut Michael Lopez-Alegria is paying for his U.S. record of 215 continuous days in space.

It's been almost a month since Lopez-Alegria returned from the international space station, but he still walks a little funny because his body's balance system is readjusting to gravity.

He's getting used to his weight and having to haul himself out of a chair, for example, instead of floating around. For a while, everything felt heavy to him.

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But that's not the hardest part of the transition, Lopez-Alegria told The Associated Press on Thursday.

"When you're in space, you're sort of in this parallel plane," he said. "It's a part of your life that is really hard to compare with the other part of your life.

"I think for the men and women that are involved in the war on terrorism, it's probably not very different. They are having breakfast with their family one day, they get deployed the next day, and while they're over there, they're living a completely different life with a completely different environment around them."

The two, Lopez-Alegria said, "don't really intersect very well."

But the spaceflight veteran is quick to say that experiencing disparate realities "is not a bad thing."

"It's just the way it is," Lopez-Alegria said. "The transition just takes some time."

While in the cosmos, the Madrid-born astronaut went on three spacewalks to upgrade the space station's cooling system and do maintenance on the orbiting outpost. Lopez-Alegria also worked on various scientific experiments.