Define homeostasis,and explain why negative feedback is preferred over positive

Negative feedback is when the effect of something results in the decrease of that original something. Positive feedback works to enhance deviation from homeostatic set point. Negative feedback works to go back to homeostasis.

Negative feedback is invariably preferred in closed-loop control systems because negative feedback results in better stability in steady-state and rejects any disturbance signals. It also has low sensitivity to parameter variations.

An example: In blood clotting, one blood factor leads to production of many other and the process continues to amplify until the blood clots. It wont be a suitable for blood regulation, because you never want to leave the set point for the body's core temperature 36.5 - 37.5 celsius. Regulation of body temperature is negative feedback.

The sympathetic system is responsible for arousal and energy generation while the paraympathetic system acts antagonistically to the sympathetic system. That said, it would be the sympathetic system that would get activated.