system
Given the following post, respond as if you're commenting on Reddit:
human
When we fall asleep what's to keep us from staying asleep? How does our body know when to wake up?
gpt
When we sleep, we are in an altered state of consciousness. We aren't consciously perceiving the things around us, but we still maintain a level of unconscious awareness, albeit the threshold for stimulus recognition is a bit higher while sleeping. So, that brings us to a couple of ways our body wakes up. We can either be awoken by external stimuli which alert our nervous system to become conscious (e.g. an alarm clock), or when no stimuli are present, our body will wake up in accordance with our circadian rhythm, which is essentially a periodic pattern of brainwaves which follow our sleep-wake routine. Our circadian rhythm is sensitive to a few factors, such as exposure to light throughout the day, how much sleep we had during our last rest, etc..