What does the title character experience while he is sleeping in Washington Irving's short story "Rip Van Winkle"?

In Washington Irving's short story "Rip Van Winkle," the titular character falls into a deep sleep following his consumption of the proverbial strange brew, initially described by Irving's unseen narrator as "a stout keg that seemed full of liquor" and "had much of the flavor of excellent Hollands." Finding the taste of this beverage very much to his liking, the perpetually irresponsible protagonist proceeds to drink a quantity sufficient to render him unconscious or, as the narrator suggests, throw him into a "deep sleep." With this development, Irving concludes Part I of his story.
With the beginning of Part II, Rip awakens from his sleep, certain that he has merely slept through the night and concerned about the reaction he will encounter from his far more responsible spouse, Dame Van Winkle. Rip's story proceeds to its conclusion, which entails his discovery that he has actually slept for twenty years and that his daughter is now grown and married, but the friends and neighbors he knew are dead.
As for what Rip experienced while sleeping, no one knows. Irving simply allows his protagonist to fall asleep and wake up two decades later. There is no sense of Rip having dreamt of anything in particular. His only experience is that of the natural aging process. In describing Rip's appearance following his long sleep, Irving's narrator notes the now-aged man's "long, grizzled beard, his rusty fowling piece, his uncouth dress, and an army of women and children at his heels...." What we can conclude, therefore, is that Rip experienced the aging process while sleeping.

Rip falls asleep after drinking a flagon of the beer with the odd, old-fashioned Dutch people he runs into in the mountains. We learn that his senses are overpowered, his eyes swim, and his head gradually droops before he falls into a deep sleep, indicating that this beer is more powerful than what Rip is used to consuming.
We don't learn anything about his sleep, such as whether he dreamed, but when he wakes up he is surprised that he might have slept all through the night. Although he has been snoozing deeply for 20 years, on awakening, he has no inkling of this. Instead, he worries about what excuse he can give Dame Van Winkle when he gets back home and wonders why his body feels so stiff in his joints, not yet associating this with aging.