Hi Timo,
Where exactly was your pain? If it was just below (or at the edge) of your rib cage, my money's on a gastric ulcer. Try to avoid acid (ex. vinegar) and spicy foods for a while. Also, NSAIDs and aspirin can be major culprits.
If the painful spot is lower, it could be the large intestine. I experienced something similar about 7 years ago, but it was in my bowel (pretty much where the appendix is). It recurred a couple of times since.
In my case, it happens mainly after intense physical effort.
Hope this helps.
