Besides myself, of course, know or have known many who fit your symptoms. Some mask their depression by many routes...alcohol, drugs, overachiever, workaholic, toy fiend, or about anything that takes the place of any real one on one relationship...even with ones self.

For me it is more cyclical than chronic...predisposed to it, drowning in it when I married (knew we shouldn't have), cyclical with hormonal cycle (I should be hilarious to be around once I hit menopause), and now dealing with chronic pain it follows the lows of that...and relationships...and fears...it feeds the fears...

I have always been fascinated by those who prescribe feeling good about oneself (intrinsic), or nothing will make one feel good...(extrinsic).
There is no line...there is a person...and there are stressors. No matter how much one may love themselves a stressor may arrive and bring with it depression...or trigger it. Life, being one gigantic stressor from the time of conception, is and never has been...a bowl full of cherries where if we do the 'right thing, marry the right person, look just right' etc. we shall be 'happy'. Some just cope with the stressors better than others...now with meds, yes, they help...so does therapy...but it does not negate the depression...

The phrase 'quiet desperation' comes to mind.