- I'm Dr. Bill Kefalas. I'm the Medical Director of the University of New South Wales Health Service. 
Stress is a normal thing for a human being. What happens in your body is that adrenaline is pumped through your arteries, and your heart goes faster, your pulse goes up, your blood pressure goes up. 
People can feel their head pounding. People can feel themselves flushed or sweaty. People can feel that their vision's not quite right. 
They can feel a bit sick in the stomach. They can have a very worried feeling in their mind. 
In say, an exam situation, we know from a lot of research that your performance in an exam actually improves as your stress level increases, to a certain point. 
At that point, and after, if you become too stressed, then your performance decreases. 
So of course that's a negative aspect of stress. The other negative aspects of stress can be that if it goes on for a long time, then you can be worried and thinking about things in a very negative way for long periods of time which can really sort of wear you down. 
It can make you tired, it can give you long term headaches. It can even lead sometimes to depression if it goes on for too long. 
As parents, when we know that our children are going through difficult times, we need to be on the lookout for some changes in behaviour, or things that they might be feeling that might signal that they're suffering from excessive stress. 
Things like, can't sleep, getting to bed too late, feeling quite fatigued, or not being themselves, saying their tired all the time, maybe not eating very well. 
They might be telling us that they've got headaches, or that they've got their tummy is playing up again, sitting in their room a lot of the times on the weekends, and when they're usually out with their friends. 
So these sorts of things we have to be mindful of, and think that that might be a sign that they're suffering from excess stress.