Twice this week we've been up cleaning up DS' vomit at 12-1am. (Tuesday morning and this morning)
He was sick over himself and just kept retching till there was nothing left (with 5-10 minutes breaks in between) and he could finally go back to sleep.
He's been a little bit off his food, but otherwise ok. No temperature.

Is it just one of those things?
It's not very nice for the poor mite (or us!)