My boy has this issue before. And doctor told me it's something regarding to nerve system energy release when a child in deep sleep. He told we didn't have to use any medicine since it's very common for undeveloped nerve system. He just ask us to turn the child before he goes to deep sleep. In this way we could wake up child a little bit without disturbing his sleep. Thus I turned my boy or hug him 1.5 or 2 hours after he falls into sleep.
The Chinese way will work too since when you call your baby's name he will be waked up a little too.
There is a medical term for this. But I forgot after 6 years. Sorry about this. Please talk to your doctor about your boy's sleep pattern. If he/she couldn't help you on this one, you may want to change your doctor.
