As the title says really. It's happened a few times now. Twice on holiday, at breakfast time when I hadn't eaten since later afternoon the day before, and at about 9pm on another day when I hadn't eaten since breakfast )lost track of time!) And again about an hour ago when I had a ham sandwich which was the first thing since about 8 last night.
The only thing I can think of is that it's too 'heavy' on my empty stomach? It's not as though I dive straight into eating something heavy and greasy, since it happening the first time i'll have something light but filling, and it still comes straight back up the minute I take the last bite!