dysthimia/ major deprssive disorder

The way in which depression is diagnosed and the various types of depression, in particular the difference between major depression and dysthimia, confuse me. I would like to ask this: how would someone who has a constant low-level feeling of depression that is interspersed with briefly passing(maybe lasting up to a fortnight) periods of severe depression be described and is there a difference between how the two things are treated?

[Charetti]

For me dysthimia is that constant low level depression and depression is the deeper stuff. Dysthemia keeps a persons baseline lower than it should be so when something bad happens, or you get triggered someway, the drop to depression is quicker.  Many antidepressants will help bring that baseline up, just have to experiment to find the right one.