My stomach was in my throat, is a nonliteral informal expression used to express feelings of anxiety or uneasiness. As the rollercoaster car slowly raised higher and higher into the air and I could see the ground moving away, my stress levels increased as I saw we were getting nearer the peak, and the inevitable stomach churning ride to come.

I've heard, my heart leapt into my throat, which means, it surprised or shocked me so much. As if my chest tightened and I could hear my heart beating in my own ears because I was so stunned by what I saw or heard. I looked it up on Google which said that you use this expression when you're afraid, but I also think you can use it when you're shocked. For example: When I couldn't find my dog anywhere, I asked my mother where she had gone. "I had to give her away," she told me. In that moment, my heart leapt into my throat and I didn't know what to say.

Context? Formal, or casual?