More often, emotions aid survival. Emotion may blossom, change course, or diminish as it proceeds. And, mere thoughts or memories can make us fearful, sad, or happy. And, relationships are one of the most potent sources of human emotional response. Physical aspects of emotions are innate, or built into the body - not normally under voluntary control.
Sugar is released into the blood stream for quick energy.
Heart beats faster to distribute blood to the muscles Digestion is temporarily inhibited Blood flow in the skin is restricted to reduce bleeding, etc. Parasympathetic branch generally reverses emotional arousal and calms and relaxes the body. It restores balance, and it helps build up and conserve bodily energy. Heart is slowed Pupils return to normal size Blood pressure drops etc. And, the Parasympathetic responds much more slowly than Sympathetic branch.