<p>HOUSTON (Reuters) - Astronaut Heidemarie Stefanyshyn-Piper collapsed twice during a welcome-home ceremony on Friday, a day after returning to Earth from a 12-day mission on space shuttle Atlantis.</p>
<p>Stefanyshyn-Piper, who was on her first spaceflight and made two long spacewalks to perform work on the International Space Station, had "a couple of small dizzy spells" while speaking during the ceremony at Ellington Field in Houston, said NASA spokeswoman Lynnette Madison.</p>