I don't think there's anything such as 'normal' depression. Some people experience situation depression after a negative life event, some people experience one depressive episode out of nowhere but never have another one, some have persistent depressive disorder, which means slightly lower mood over a span of years.
Depression comes in various shapes and sizes and levels of intensity. But clinical clinical depression is considered the strongest, most severe form of depression, and usually entails more than a couple of episodes. I recommend reading these article for more info:
https://www.health.harvard.edu/mind-and-mood/six-common-depression-types