The part of the brain most sensitive to a lack of sleep is the amygdala – the seat of anxiety and big emotions. The amygdala has the very important job of scanning the environment for threat. When it senses what might be a threat, it surges the body with a mighty cocktail of fight or flight neurochemicals. If there is a threat, this is excellent, but if there is no need for fight or flight action, the neurochemical fuel builds up and anxiety happens. This is where sleep comes in. A tired brain will struggle to tell the difference between a threat and a non-threat, so it will tend to hit the panic button more than it needs to.
During adolescence, the hormone that makes us sleepy – melatonin – is released up to two hours later than it is in children and adults. Adolescents need at least nine hours of sleep (ten is gold) but they might not even feel like winding down until 10 or 11 pm. Combine this with early morning starts for school, and you can see where this is going to end up. The more tired they are, the more reactive their amygdala will be, and the greater the potential for anxiety.