One of the major themes is the inevitability of change. Rip goes to sleep not expecting anything important to have happened during the night; upon waking, he discovers that he has lost years of his life without even knowing it. Rip never thought anything would change; he thought his life would continue as it had in the past without any real difference. However, change occurs without human intervention, and the passage of many years is not necessary to have great changes made.
The very village was altered: it was larger and more populous. There were rows of houses which he had never seen before, and those which had been his familiar haunts had disappeared.
(Irving, "Rip Van Winkle," bartlby.com
Rip finds a new, peaceful existance in a place which was his home, but is now as foreign as any far-off land. His surprise at the amount of time that has passed is easy to understand, but can be felt by people in ordinary circumstances as well; it is easy to wake up and realize that the last few years have flown by and things have changed. Rip's experience was more dramatic than most, but shares the sense of loss, confusion, and denial.