Anony, from MY understanding of depression this up and down isn't regular depression. I've been having the same thing (though for the past nearly week have felt good with NO ups and downs!) and was convinced it was something like bipolar or borderline, because these are disorders that have 'mood swings'. My therapist told me otherwise. But if you read the diagnostic criterea for depression it states that you must have been in that depressed state, constantly, for I think a period of 12 days. But I'm no doctor.
Other people will tell you it's normal for depression, and it may well be. But I think.. no harm in getting an analysis or something, or just talking to your doctor/therapist and seeing how they can help you.