mind.org defines depression as: a low mood that lasts for a long time, and affects your everyday life.
We all have times when our mood is low, and we’re feeling sad or miserable about life. Usually these feelings pass in due course.
But if the feelings are interfering with your life and don't go away after a couple of weeks, or if they come back over and over again for a few days at a time, it could be a sign that you're experiencing depression.
When we experience chronic stress (when our bucket is overflowing), or when we experience a stressful life event like loosing a job, these can trigger depression. Chronic stress in particular, leads to elevated levels of cortisol, which is often referred to as the stress hormone, and reduced levels of serotonin and other chemicals which have been linked to depression.
When we are functioning healthily these chemicals help maintain biological processes such as like sleep, appetite, energy, and sex drive, and permit expression of normal moods and emotions.
The mood self-assessment provided by the NHS can help you determine if you are anxious or depressed. Please note this is not designed to replace a GP. If you need further medical advice please contact your GP.