In other words, it is a subtype of depression that is specifically triggered by the change of seasons, and occurs at the same time each year in individuals who have normal mental health throughout the remainder of the year. It is more common during the autumn or winter months - hence also the name 'winter depression' - and the symptoms usually subside by the start of spring. This is different from the 'winter blues' - a milder from of SAD - that causes temporary low mood during the colder months, but it does not have the same severity or impact of SAD which can result in a certain degree of disruption to daily life.Another form of SAD exists called 'summer depression' which is a mood disorder that contrastingly takes place at the start of the summer and ends by autumn or winter, but this is a much less common version of SAD with an incidence rate of approximately 10% of total number of cases only.