"I was just so super excited that I went home and went to bed," she told PEOPLE Thursday at Las Vegas's Vanity during a party honoring the issue. "The next morning I had to wake up at seven o'clock in the morning and do a bunch of TV shows. I had dinner then went to bed."
Granted, there was a party to mark the publication of the issue, but Shayk, 25, didn't last long there.
"It was so surprising that I had to sleep to realize I was on the cover," she said. "When I saw it, I was like, is that really me. I have bad vision. I still don't believe it."
With the coveted cover spot one of the most closely guarded secrets in publishing, Shayk, who has graced the inside pages of the famed issue five times, said she had no idea she was the cover model until the moment it was revealed.
"It was the greatest day of my life, my biggest moment," she said. "It's like waking up in a dream."