Doctors and other medical professionals often call depression "clinical depression". This distinguishes it as a diagnosable medical condition, as distinct from the general low mood that everyone experiences from time to time, or dysthymia. 

The symptoms of depression may be as follows:

• Persistent sad, anxious, or "empty" mood
  
• Feelings of hopelessness, pessimism
  
• Feelings of guilt, worthlessness, helplessness
  
• Loss of interest or pleasure in hobbies and activities that were once enjoyed, including sex
  
• Decreased energy, fatigue, being "slowed down"
  
• Difficulty concentrating, remembering, making decisions
  
• Insomnia, early-morning awakening, or oversleeping
  
• Appetite and/or weight loss or overeating and weight gain
  
• Thoughts of death or suicide; suicide attempts
  
• Restlessness, irritability
  
• Persistent physical symptoms that do not respond to treatment, such as headaches, digestive disorders, and chronic pain

Not everyone who is depressed experiences every symptom. Some people experience a few symptoms, some many. Severity of symptoms varies with individuals and also varies over time, however, a person with at least three of these symptoms over a period measured in weeks is regarded as meeting the diagnostic criteria for clinical depression.

In some cases, a person may be depressed but exhibit none of these symptoms. They may seek to avoid facing issues by throwing themselves into other things, like work, a new relationship or an activity undertaken obsessively.

Remember, a medical opinion is important because other conditions, such as viral infection or hormonal changes, can mimic the symptoms of clinical depression. Moreover, your GP is well placed to advise on things you can do to help yourself and types of treatment, if a diagnosis of depression is confirmed.

There is no doubt that clinical depression is a condition that affects both mind and body. In severe cases it can have a devastating effect on a person's life and even bouts of what we might consider to be "moderate" clinical depression can be extremely incapacitating, affecting (albeit temporarily) our ability to lead a normal life.