It sounds like your wife's hormones are still settling down after her pregnancy, and as you suggest, it is a post-pregnancy phase, partly physical in origin - the hormones, and partly emoptional, the feeling of responsibility for another life. It will settle down, but if the dreams persist, you would be advised to contact your GP or midwife for a chat, to put your minds at rest. In the mean time, enjoy the wonderful experience of your new baby, and don't worry!