Is this simply a physical problem? I doubt it.
When I say, ‘my stomach is in a knot’, it usually means I am dealing with strong, difficult emotions, experienced as tension in the abdomen. After 15 years of consistent meditation practice and many silent retreats, I can now detect even subtle emotions as body sensation: fear has been a companion, and anxiety, its offspring (which I define as amorphous fear), has been hitching a ride every day and night since the beginning of February. It is now mid-June.