A team at UCLA gave 20 volunteers a series of mental exercises when they woke during the night and in the early morning for a few days aimed at inducing a 'half-dreaming' state.
And it worked, with more than half the volunteers experiencing at least one out-of-body experience as a result - and seven of the 20 reporting having made visual contact with UFOs or extraterrestrials.
The sensations they described were identical to those of accounts by 'alien abduction survivors', says the team.
"I made myself open my eyes and I saw a typical-looking extraterrestrial at the other end of my bed: it had a huge head with large eyes, a small body with thin arms, and dark-green skin," said one volunteer.
"Meanwhile, everything was even more realistic in terms of sensation than in my normal waking state. Once I understood that there was no turning back, the fear fell away."
The results show that such experiences are a product of the human brain, the researchers claim.
"We tried to right a common misconception with this experiment - the issue at hand isn't extraterrestrials, but hidden human abilities," says experiment author Michael Raduga.
"If you've encountered UFOs or aliens after sitting or lying down, it can now be unequivocally stated that you've had a spontaneous out-of-body experience. We have proven this."
The finding is unlikely to convince the thousands of Americans who claim to have been abducted by aliens every year. It's a belief that's not confined to the US, though: two years ago Japan's first lady, Miyuki Hatoyama, claimed to have visited Venus in the company of aliens.
The full report is here.