Please refer to the stress Toolkit:
stress toolkit for local authority schools
stress toolkit for academy schools
Both titled Health and Safety Toolkit - Stress and Wellbeing. The toolkits include three questionnaires that can help with understanding the causes of stress. It may be helpful to make a prompt referral to occupational health, to support the member of staff. As part of the referral, include a copy of the stress documents to be discussed at the appointment. Please see the question relating to making an occupational health referral for more advice.
On occasion, particularly where the potential 'stressors' are already well understood it may be helpful to move straight to a joint discussion to develop a 'stress management action plan'.
In all cases, HR advice should also be sought at an early stage.