Final answer:
Sympathetic nerve activity generally decreases during both NREM and REM sleep, reflecting the body's shift to a restorative state, as opposed to the 'fight or flight' response triggered by the sympathetic nervous system during wakefulness.
Step-by-step explanation:
Sympathetic nerve activity decreases from both Non-Rapid Eye Movement (NREM) and Rapid Eye Movement (REM) sleep in some body areas. During NREM sleep, especially in the deeper stages, the body experiences a reduction in sympathetic activity, which corresponds with a deceleration in heart rate and respiration. Conversely, during REM sleep, which is associated with vivid dreams, there can be moments of increased sympathetic activity; however, overall, muscle tone decreases and activity in areas such as heart rate and respiration may still generally be lower compared to wakefulness. It is essential to distinguish between the sympathetic and parasympathetic nervous systems, as they often have opposing effects on various organs and systems. The sympathetic nervous system is typically involved in the 'fight or flight' response, heightening the body's state of arousal and readiness for action. In contrast, the parasympathetic system is often termed 'rest and digest,' allowing the body to recharge and maintain lower levels of exertion.