I think yesterday's stomach ache was completely a by-product of being on the heaviest day of my period, cramping etc.  Somehow I just didn't recognize the connection - it felt like it was more in my stomach than usual -- like a kind of undigested-food-gassy feeling.
But today, I'm 100% fine - no cramps, no stomach ache, everything is grand, I'm feeling good.
Probably a mental boost of goodness is coming from the scale reading this morning - 140. After returning from my vacation last weekend to see 144 on the scale (having been at an all-time low of 138 only the week before!) I wasn't pleased.
In all reasonableness, I would have to attribute the astonishing drop to several aspects of the body's weight mysteries:
1. The water retention from the period was at maximum on Sunday, now it is completely gone
2. Now that I'm not gorging on pancakes and carbs and generally huge quantities like I did at Club Med, my intestines are emptying out again, the water retention that comes from eating junk has subsided, and the slight dehydration affect that comes from eating low-calories (1200) has also kicked in.
In essence -- it's all about losing excess water!  Probably only a fraction is from the lesser amount in the intestines.