First, your heart speeds up: you can feel the pounding through your chest. Then your hands grow clammy and cold. Finally, a wave of nausea sweeps up, and you feel as though you might faint.
For an anxious child, this feeling of fear and panic can be a daily occurrence, brought on by nothing more than a walk down a school corridor, or being called on to read out loud.
To help teachers deal sensitively with anxious pupils, the charity Anxiety UK has produced an information pack for teachers that it has sent out to schools.
This offers advice about how to identify and support anxious pupils. For example, it suggests that teachers should allow anxious children to sit where they choose in the classroom: some prefer being by the door, others at the back, where no-one can see them.
Teachers should also be aware that anxious children may not be able to cope with being asked questions in lessons, or experience difficulty when eating in public or using communal toilets.
A pupils' guide explains the causes of anxiety and how to combat it in accessible language.
One in six people experiences an anxiety disorder at some point. In an average school class, five pupils are likely to have had problems.
And school is likely to be the focus of many of these problems. Anxious children often fear crowds, so that noisy lunch and assembly halls can be terrifying.
Many are distressed by change, so the arrival of a new teacher can also be cause for alarm. But anxiety is difficult to spot.
Anxious pupils often defuse a difficult situation by misbehaving, so their symptoms can be indistinguishable from general behavioural difficulties. Others can seem merely shy or lacking in confidence.
Charles Ward, chief executive of the Association of Educational Psychologists, believes that schools should therefore try and minimise anxiety for all pupils. "All children, all people, get anxious from time to time," he said. "Some are anxious about being bullied. And there's a lot of anxiety around examinations. Teachers need a whole-school policy, to make sure anxiety levels are reduced before they become problematic."