Final answer:
During N3 sleep, a phase of deep sleep, individuals experience low frequency, high amplitude delta waves, and their heart rate and respiration slow notably.
Step-by-step explanation:
People in N3 (R&K Stages 3 and 4) sleep, also known as the deep sleep stage, is characterized by low frequency, high amplitude delta waves. During this time, an individual's heart rate and respiration slow dramatically, making it more difficult to awaken someone. Importantly, this stage is crucial for feeling rested, and disruptions in it can lead to the sensation of not feeling refreshed upon waking. Individuals in N3 sleep exhibit some of the deepest and most restorative sleep, which is vital for learning and memory. People experiencing alpha brain wave activity during this stage may report not feeling refreshed, indicating the significance of this stage for overall sleep quality.