Teaching is a very stressful job and stress is the number one cause of many teachers leaving the profession within their first year. Stress can be caused by a disruptive class. Teacher not having control and therefore not dealing with situations as they should, too much workload and not enough support from head teachers or colleagues. If you are a teacher and are feeling under pressure in your current job then there are places you can go and people you can speak to, to get support and advice. The NUT _Nation Union for Teachers have recently set up a helpline dedicated to teachers who are in need of this type of help. There are also some great online groups and forums you can join to share ideas, views and opinions as well as asking for support.
Your head teacher should also offer you support and advice although it may be difficult to get time to speak to them one to one.