MARIE OSMOND opened up this morning to our MARY HART about her shocking collapse after performing the samba on Monday night's "Dancing with the Stars."

"It's nuts," she says. "I feel bad that it happened!"

Marie, who says she's fine now, tells Mary her theory as to why she fainted. "Right at the beginning, I started getting light-headed. The only thing I can think of is I have allergies, the air quality is terrible, and I couldn't get my breath."

And as soon as she woke, it took her seconds to realize what was happening. "I wasn't quite sure what was going on and then I saw everybody. I saw my kids, I saw TOM [BERGERON] and I think I said, 'Oh, crap'"!