What a lot of people don't tell you about severe depression is that once it passes, and you find happiness within yourself, it is extremely difficult to be brought back down to a low again. Keep in mind the key words, however, that I added within that text: after you find happiness "within yourself."
Happiness at its core - I've found in my own experience with severe depression - is a complete peacefulness with oneself. That's it. Honestly. You can't be dependent upon your family, your friends, or your romantic partner to be happy, and most importantly you can't be dependent upon your own flaws or failures.
At the root of my own depression was a continuous sinking feeling that I would never be independent. The most alarming part of it was that it was wholly unreasonable, yet I could not look past the anxiety that I'd probably end up so in debt that I'd be on the streets, and I didn't once during the spell think that I was being irrational. After failing to see myself after almost 4 years working toward an English literature degree, all to find that my passion was for linguistics and speech pathology, I realized how much more of a financial burden it would put me under to go another few years to obtain a Master's as well. I was so ashamed that the depression brought my mood so low, my attention to anything else in my daily life so miniscule, that my confidence was absolutely gone. I honestly feared for the integrity of my life. I had never thought of my phone being able to call out to my mother to be so much like a literal life line, nor did I ever think I needed a life line.
I never thought my academic success and fear of disappointing others would ever bring me to thoughts of suicide, and feeling as though my life was worthless - but here I am now, able to tell my story of severe depression exactly as it happened; truly anything in one's life is enough to push them over the edge if they view it as such, because so much is dependent upon perspective. Everyone's perspective of things is different, all based on individual experiences.
I'm writing about this not because I crave sympathy for an experience in my life that has already come to pass. I'm writing about this because I know year-ago-me would have liked to have read these words, and known that future-me was going to come out such a stronger person - resilient to the point now that little may phase me. I've found such peace in my newfound happiness that bad romantic relationships, financial strain, and family issues have little impact on me. I find now that I can feel everything again, and I CANNOT stress how important that is to me. If I recall strongly, in the far reaches of my mind I pushed back that numbness - that complete lack of feeling that encircled my entire being for three tireless months that stretched into years. My mind won't even allow me to touch that state of mind again, but what it does allow is for me to be reminded of it when I see, likewise, the faces of others who are currently going through the same pain. I'm writing this because I want those people to listen - listen as much as you can. And if like me you're currently so incumbered that you cannot pay attention, reread this all.
YOU have the power within yourself to feel again, too. Nothing particularly significant is currently going on in my life, yet I'm happier now than I've ever been. It truly depends on how you view yourself and your place in this world. The past 6 months I've begun rebuilding my conscious by loving myself first, as well as realizing where I fit in with my family and friends. I broke up with the boyfriend who brought me down, I took many science classes to get me toward the degree I know will make me happy, and I've worked long and hard at a job that financially supports my decision to go back to school for another few years. I've done all of this for myself, knowing that a happier me would come as a result, and would benefit as well those who surround me.
Nothing is better than feeling at peace again with yourself after a long emotional absense, and seeing afterward all the things you missed, so that you're that much more attentive to those things - that much more appreciative.
I'll never take for granted again the sweet little moments in life that I'm able to enjoy now, because I went through such a significant bout of depression. I came out of that dark period in my life better off for it, and I know it is within anyone else's capabilities to do so as well. Like any other monumental step in life, if nothing else take your sad (or apathetic) times as learning experiences, and realize that future-you can never again be led to believe the same things that brought now-you to that dark place.
If you think and truly believe that way, the only way to go for you is up.