Have you ever cried in your sleep? And what type?

I know there are three reasons for sleep crying out there, some more extreme then others. The first one, a simple nightmare. Of course, you can wake up from a nightmare so scared you end up in tears. It's just that simple. The second reason, is probably the most extreme. Sleep terrors begin during the REM stage of sleep. (R.E.M. Is the fourth and final stage of sleep and stands for Rapid Eye Movement stage) During sleep terrors, the person dreaming will often scream, thrash, cry, and even possibly run. Often times, they never remember the dream or what they did. The final reason for crying in your sleep is actually called Dream Crying. This one happens when you feel an intense, unrelenting sense of either sadness or joy. (Both feelings where you cry, obviously.) Dream crying is how I have experienced crying in my sleep. Every time it was because of a sense of extreme sadness. The loss of a loved one through death, an extreme breakup, a really bad accident, etc. What I'm really interested to know, is how often it happens to you. Why do you think it happens? And what type is it?