I present to you a stressed person, according to Psychology Today:
Scary.
Yet, I wonder, what really is stress? I decided to have a conversation with the internet to investigate this matter.
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F: Government of Victoria, as an important authority on health matters, what is this concept which is referred to as stress?
Better Health Channel: ‘[s]tress is a feeling you have when you face a situation you think you cannot manage’.
F: Interesting. Stress is a feeling of being unable to cope. That really clears things up!
Psychology Today: We thoroughly object! Stress is simply a reaction to a stimulus that disturbs our physical or mental equilibrium.
F: That seems like a slightly different definition. What about you, (US) National Institute of Mental Health? How do you define stress?
NIMH: We are of the opinion that both the previous definitions were too specific. Instead, we say that ‘[s]tress can be defined as the brain’s response to any demand’.
F: … Now I am confused again. Apparently, there are many definitions of stress. It can refer to a specific feeling, a change in either mental or physical equilibrium, or just any non-specific human response to a demand. If mental health experts cannot agree on a definition, how do I know what stress is?
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http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/stress
https://www.psychologytoday.com/basics/stress
http://www.nimh.nih.gov/health/publications/stress/index.shtml