Maybe the surprise was too much for the fan to handle, and his legs buckled.
Lady Gaga fell from the stage when the man called Jack, whom she had invited to go up on stage before jumping into his arms, lost his balance.
The incident occurred at a show in her Las Vegas residency on Oct 17.
Videos posted by fans showed her team rushing to help the two, and Lady Gaga, 33, was able to get back on stage to continue her act.
"It's amazing. We love each other so much we fell off the stage. We fell into each other's arms. We're like Jack and Rose from Titanic.
"I suppose we should have some tea after that," Lady Gaga jokingly told the audience.
"It's not your fault," she reassured Jack.
"Could you promise me something? Could you forgive yourself right now for what just happened?"
Showing how tough she is, she later posted a photograph that showed her enduring an ice bath, part of her post-show recovery routine that also includes a hot bath for 20 minutes and wearing a compression suit packed with ice packs for 20 minutes.
But just to play it safe, she also went for a full body X-ray, with the results confirming that there was nothing to worry about after the fall.