I, too, meditated for 10-30 minutes a day for about a year before attending a Vipassana retreat and had the same experience. Even upon returning from the retreat and meditating 30 minutes in the morning and 30 in the evening, I was not able to replicate the experience of the course. I returned and served for three days last fall, during which time I meditated for 3-4 hours a day and began to approach the feelings once or twice.