I wouldn't worry about it too much. I don't get those kind of dreams very often any more but when I do they are usually very strong and very vivid. And normally they end before things get really heated, so, like you, they don't last very long. But I think it's normal for guys (I'm not too sure about women) to have sexual dreams, regardless of the content. I think the younger you are...or the hornier you are...the more frequently you will have them. They are, after all, only dreams, so I wouldn't be overly concerned about them. I guess if I didn't consider myself to be a BL and then had a dream about having sex with a young boy, then I would be worried, but since I know exactly what I am sexually attracted to, it doesn't surprise me or concern me too much when I dream about it occasionally.