Visions can appear so real that you think that you're living through the vision, and actually experiencing the actions in a physical sense, whereas in reality you could just be lying in bed. That's assuming the vision seems to involve physical activity on the part of the person having it.
Those sorts of visions also take place very quickly - a vision in someone's mind which seems to encompass an entire weekend's activity might only take a few seconds in real time.
Saint Paul could have been "snatched up" to heaven in visionary form and not real form. But it would appear so real he wouldn't know if he'd actually been there or not. The only way he'd be able to tell would be if a witness had been present at the time, who could confirm if he'd disappeared for example.
To actually go to heaven in person he'd have had to temporarily disappear from this earth or at the least bilocate, as Padre Pio had a reputation for doing.
As a particular pastor said to me once, "There's a very strange psychic world out there!"
