Final answer:
Stage 2 sleep marks a deeper level of relaxation with the presence of sleep spindles and K-complexes, but the body enters a state of deep relaxation characteristic of stage 3 sleep, also known as deep or slow-wave sleep, identified by low-frequency, high-amplitude delta waves.
Step-by-step explanation:
As we move into stage 2 sleep, the body goes into a state of deep relaxation. Stage 1 sleep involves a transition from wakefulness to sleep and features a mix of alpha and theta waves, but it is stage 3 sleep, often referred to as deep sleep or slow-wave sleep, that is characterized by the presence of delta waves. These waves are of particularly low frequency (less than 3 Hz) and high amplitude, reflecting the deep level of relaxation and decreased physiological activity, such as a significant slowing of the heart rate and respiration. This is also the time when it becomes much more difficult to awaken someone. Additionally, sleep spindles and K-complexes appear during stage 2 sleep, indicating deeper relaxation but not as profound as in stage 3.