Crossword: The demand for sleep

4. A naturally occurring and reversible altered state of consciousness, characterised by a reduction in awareness and responsiveness to external surroundings
6. A type of sleep characterised by quick darting of the eyes behind closed eyelids and an increase in physiological activity
8. A state associated with being aware of our internal and external environments
10. The awareness of your own internal mental processes, including your thoughts, feelings, sensations and perceptions, and your awareness of the external world around you
12. Biological processes that coordinate the timing of body activities over a period of less than 24 hours
16. Any state that differs in awareness when compared to normal waking consciousness
17. A hormone that induces drowsiness and decreases cell activity
18. A subjective self-report tool used by a person to track their own sleep and wake patterns

1. A technique that detects, amplifies and records the electrical activity of the muscles controlling the eyes
2. A master body clock in the hypothalamus that regulates body activities to a daily schedule of sleep and wakefulness
3. A sleep study tool used to collect qualitative visual and audio information about a person’s sleep
5. A technique that detects, amplifies and records the electrical activity of the brain
7. A concept that cannot be objectively observed or measured directly through the collection of data, but is widely understood to exist
9. An environmental cue such as light, temperature and eating patterns that can synchronise the body’s circadian rhythm
11. A type of sleep characterised by a progressive decline in physiological activity
13. Biological processes that coordinate the timing of body activities over a 24-hour period
14. A line graph that represents the stages of sleep plotted against time
15. A technique that detects, amplifies and records the electrical activity of the skeletal muscles