People who are never depressed are probably time bombs. Depression is a necessary component of a healthy personality; it is the mechanism by which neglected priorities command attention, and if played well, often precedes a welcome and significant change in your life. It is nothing more than a signal, a beacon to summon focus; once the cause/problem is determined, and progress comes, the depression should disappear.
The big problem with depression is that people are often afraid of it, and try to avoid experiencing it; this negative valuation locks the depression right in, enforcing worry and negativity, impacting and embedding it, keeping it apart from the required attention. Then, the changes don't come, and it just makes itself worse.
Unfortunately, negativity is an extremely compelling space, a short and stable instruction set (anything at all, multiplied by NO) which readily compounds: it's easy when one thing brings you down to stir up all kinds of unpleasant supporting thoughts. And, it's far easier to have something bring you down than it is to snap out of a bummer, but with conscious effort (admit it, examine it, work it on out), you can usually move on. Getting to a place where you're willing to make that effort is the hard part; often when you are down you are so discouraged that no motivation is forthcoming. The dark veils go up, no light gets in, nor any air. It can so distort perception, disallowing any hope; this can sometimes be an effective defense mechanism in the short term, keeping volatility down, but it can become a too-familiar posture, no longer a tactic but a mandate. People can get so in the habit of keeping themselves safely protected in an unavailable state that this posture becomes much like an ego, fighting to survive, but at the cost of the host, sometimes with fatal results.
For those moments when ending it all seems an option (that's the price of intelligence): the voice that speaks then, bitchy, moany, tired of it all, let THAT voice/ego go ahead on and give just itself all the suicide it wants, piss off and stop hogging the microphone, let curiosity have a chance. If it finds consciousness so damned inconvenient, then stop occupying it, deal? Really, whenever the pissy voice is predominant, wallowing in pain and loss, give it full permission to extinguish itself; there are plenty of other options/modes available, all happy to jump in. And you can even go so far as to say that every moment after that is therefore hereby the bonus round, nothing to lose.
The catch is you can't just turn off depression; you have to displace it with something else. You can call it "replacement thinking": whenever you feel yourself being pulled into the same loops and spirals, have at the ready other thoughts and directions that you can choose to pursue instead. Do you have a friend that never let you down? Or a relative? Or is there something that usually puts a smile on your face? Make a list, have it ready. Nothing will work all the time, bit it's a start.
A strange trick, oddly enough works sometimes: make a big smile with your face, work the eyes, everything. Hold it for at least 15 seconds. If your mood isn't toooo heavy, this will actually make your brain think it's happy, and you will fell a distinct shift.
Worry is very useful; it tells us where to look. Then you put awareness there, and move into whatever's next: planning and action. Depression is the same; when it happens, open to it easily, learn to find its root as quickly as you can, and move on. You'll have plenty of chances to practice. Learning to just recognize and accept it is a good enough place to start.
see also Basic Problem Solving
"All depression has its roots in self-pity,
and all self-pity is rooted in people taking themselves too seriously"
____________ -Tom Robbins, Fierce Invalids Home from Hot Cilmates
tell me that on a day when I'm down, and you might get an earful, but yeah, it's generally apt.