Headaches, upset stomach, and hives are examples of a/an reaction to stress.

Headaches, upset stomachs, and hives are classified as acute reaction to stress. Acute means temporary or short term but shouldn't be tolerated in the long-run and must be dealt accordingly in order not to aggravate the situation. Headaches might lead to migraine or upset stomach might lead to intestinal problems so as early as possible this must be treated immediately.