Anxiety happens for a variety of reasons but regardless of the source, the physiological response to the anxiety triggers a complex release of hormones and neurotransmitters into the blood stream. This creates the "I've got to get out of here, right now or the I feel totally frozen and can't move" sensation. Lack of focus and restlessness are other common symptoms. Everybody has a different unique response.

GI is gastro-intestinal track. So your stomach, intestines, etc.

The aforementioned involuntary chemical release that happens affects the GI system which leads to the nausea.

Hope that made some sense I wrote it quickly. Lol I'm mildly hypomanic as I'm coming off of risperdal.