After thinking harder on this, I remember that in my first experiences with Nal (up to the 10th one, I guess) I felt "something" in my stomach, it wasn't a stomachache at all, it was more like the sensation of hunger, pretty soft. It wore off a few experiences later.
Lately I've felt some light tachicardia (when your heart beats faster than usual), but nothing severe. Not scary at all.
These symptoms concern me, of course, but the benefits I have with the Sinclair Method widely compensate them. For example, I had a binge last friday night* in which I consumed six cans of beer -- trust me, that IS a great advance for me -- and on the next day I was healthy enough to ride around the neighborhood on my motorcycle. So good, folks, SO good...
* SIDE NOTE: Come to think of it, I did hear Kate Perry's
Last Friday Night on that binge!

lol