Simply being sad does not qualify for depression
. Many untoward event we face often leads us to feel sad but it does not mean it is depression. To labelled as depression it should be persistent and pervasive for most part of the day for almost everyday leading into some impairments in personal or socio-occupational functioning. In every day life once in a while every body feels some depressive symptoms but not depression. Since you are working well chances are less that you are having clinical depression, at most you may have dysthymia
a condition where very mild symptoms of depression is felt.
Hope i answered your query.
Hope you will enjoy life.