Stress isn't necessarily a bad thing. Acute stress can be positive - it mobilises our resources, ready to respond to a specific and immediate danger - but as Professor Stephen Palmer, of the Centre for Stress Management says: "The original fight or flight response was very useful if you were running away from a tiger, but when stuck in the office, with your computer crashing or 50 emails to download, it doesn't really help you." Long-term or chronic stress drains our physical and mental resources and can lead to anxiety and depression, not to mention ulcers and high blood pressure - and has even been linked to diabetes, heart disease and cancer. So why do some people suffer from stress more than others? "Stress occurs when pressure exceeds your perceived ability to cope. So it is not just external pressure, such as reaching deadlines, that triggers stress, but whether you believe that you can cope with a situation that you perceive as important or threatening," explains Professor Palmer. The key to dealing with stress, he suggests, is not trying to get ever more done but changing your attitude to perceived stressful situations - and of course, learning how to switch off, which for many of us is easier said than done. So why can't we just 'switch off'? Stress is now the most-common cause of workplace absenteeism - which in total costs the UK economy £17 billion a year - and money worries and job insecurity in the current economic downturn have only made matters worse. More than ever, we don't want to appear not to be coping - especially when our name could be on the next round of redundancies. Work emails that ping into your inbox at the weekend, texts received after midnight, surfing the internet in bed - advances in modern technology mean we're constantly connected, which only adds to our guilt if we don't respond to work requests that instant. Often, the belief we should read and respond to queries immediately is a pressure we put on ourselves - but being available 24/7 is self-defeating and impairs our performance. It's not just work emails either. Our obsession with social media only fuels our desire to be permanently 'plugged in'. "Messages are sent at super fast speed on Twitter, you can post something on Facebook and five minutes later there are hundreds of comments. "If you're not in the loop, it's easy to feel left out of the conversation, which can lead to feelings of anxiety and stress," says psychologist Susan Quilliam. The solution? Take control and literally 'switch off' at weekends and evenings. "If you perceive yourself to be in control of a situation or life in general, you will suffer less stress, anxiety and depression compared with others who do not see themselves in control," says Professor Palmer. So take his advice and hit that off button. Unless you're paid to be on call, disable the roaming device on your smartphone and keep the laptop unplugged. It may feel strange at first but make it a habit and you could reap the rewards. According to research by the 20th-century psychologist Hans Selye, it takes only three weeks of working in a certain way before we adopt that way of working as normal. This could be a negative pattern of behaviour, such as working through lunch, or a positive one - like switching off devices as soon as you leave the office. What you perceive to be true about a situation has an impact on how you feel and act towards situations, problems and general life events. As the Roman emperor and Stoic philosopher Marcus Aurelius wrote in his Meditations: "Everything is what your opinion makes it, and that opinion lies with yourself." Say, for example, you have to give a presentation at work. If you feel confident in your abilities, you may be looking forward to it - but if you perceive the situation as challenging or think that you can't cope, it becomes a source of great stress. "If their perception of their ability is quite poor, they think, 'I'm going to screw up, I haven't the skills'. So, the perceptions even creep into the perceived pressure, your perceived resources and ability to deal with things," explains Professor Palmer. According to Professor Palmer there are four types of thinking that largely cause stress: rigid demands such as 'musts' and 'shoulds'; awfulizing such as, 'Life is really awful'; low frustration tolerance, eg 'I can't stand the pressure of work'; and damnation of self or others, eg 'as I failed my exam, I am a real failure as a person'. "When I listen to people, there's a whole range of things they say to themselves when they're getting stressed. 'I must perform well.' This is a common internal pressure people put on themselves. Yes, employers may want you to perform well, but in reality often the pressure is coming from within the person," says Professor Palmer. "Often they label themselves, 'if I don't perform well, therefore I am a total failure'. Another phrase I hear clients say is, 'I can't stand it, I really can't stand it any more.' It's amazing how stressed they can get with this kind of thinking - when you say that in a stressful situation, you are lowering your tolerance for dealing with it. "Instead of saying, 'yes, maybe I'll do my best to deal with it ', you say, 'I can't stand it any more ', and so you're less likely to deal with it. And, of course, you get more frustrated and more stressed. "Another belief that follows on from here is, 'Oh my God, it's awful.' This is called 'awfulizing'. Although the situation may be bad, they describe it as 'really awful, terrible'. Then when you ask the person, what is so awful, you discover that they have only missed a deadline. It was not life or death after all." Finally, it's not just the words we tell ourselves in our head that can exacerbate stress, but the images we play out in our mind's eye. Replace images of the presentation going horribly wrong with a positive image of you performing well under the pressure. You CAN change your thinking If any of the above thought patterns sound familiar, don't worry - there is something you can do. Rational emotive behaviour therapy, devised by the late Dr Albert Ellis, is a system of counselling which aims to show how our beliefs - namely our inner dialogue - affects our lives. As Dr Ellis once said: "If people look at what they are telling themselves, look at their thinking, at their irrational beliefs and self-defeating attitudes, they can change them to preferences instead of absolute musts." If you find it hard to break old thought habits, a course of cognitive behavioural therapy could help or simply try replacing negative mental phrases with positive ones. "If you have a negative thought, try singing it to yourself," suggests Susan Quilliam. "It makes it sound amusing, so it loses much of its emotional meaning and impact." Distraction techniques can also work wonders. Instead of thinking about a stressful situation and then 'awfulizing' it, think of something else instead. That distraction could be meditation or repeating a positive word mantra or phrase - do it correctly and your mind isn't able to worry at the same time. There are many other techniques that will temporarily calm you and your body. "In Jacobson's relaxation technique, for example, you focus on relaxing your muscles. But you can also think of pleasant scenes - a running brook, the waves of the ocean or something pleasant in your life - and this relaxes your body and distracts you mentally from your over-concern about your problem," Dr Ellis advised. While distraction techniques are useful they won't solve the problem entirely, as the thoughts that created your panic are likely to return.