Final answer:
Variations in consciousness can be attributed to biological and circadian rhythms, and the different sleep stages that influence brain wave patterns.
Step-by-step explanation:
Two factors that allow for variations in consciousness are biological rhythms, particularly circadian rhythms, and changes in brain wave patterns during different sleep stages. Our biological clock, which is often aligned with our external environment, is influenced by cues such as light, affecting our circadian rhythms. Disruptions in these rhythms can lead to changes in our state of consciousness, including sleepiness or insomnia. The brain goes through various sleep stages, such as REM and non-REM (NREM) stages, each with distinct brain wave activities. For instance, delta waves dominate slow-wave sleep (stages 3 and 4), whereas REM sleep is associated with rapid eye movement and dreaming, both affecting our level of consciousness.