or sometimes first thing in the morning.
It's always happened, ever since he was a tot (he's now 13) perhaps 3-4 times a year. (so not that often really)
He'll be fine the following day, happy, lively, hungry just his usual self. Because of that I've never taken him to the doctor and we very rarely go, so it's not like I could mention it when there about something else. By morning there's nothing to see/tell but I have been scared by a friend who has recently discovered that the "nothing" she wasn't worried about in her DS turned out to be something quite serious which should have been treated ages ago 
Is Ds "normal"? Should I mention it to Dr?