Some time in the 90s, I think mid, there was a fantasy trilogy where a man was transported in some sort of fairie circle from the woods near his home to a type of medieval world. I know that the characters that knocked him out used darts to knock him out and those characters were small, more what would be considered "brownies" or such if discussing fairies. He had to do some sort of quests in all three books. I also remember that he aged in the medieval world but not his own, so if he stayed too long, it would be noticeable when he returned home. In I think the 3rd book of the series, he had a fiancee that the brownies also knocked out but weren't going to take but he grabbed one and threatened to crush its head if they didn't but would never do it.

I know this isn't a whole lot of detail, but if anyone has any idea of the series or author, please let me know.