my stomach is tied up in knots

My stomach is tied up in knots is another way of saying that you are feeling very nervous or anxious and can actually literally feel it in your stomach. When you get very anxious or nervous, you get what is often called nervous stomach where it my feel like butterflies in your stomach or feel like your stomach is tying up in knots. In actuality, it is simply your central nervous system causing you to feel a certain way from the nerves.