I experienced my first Major Depression at age 14. That's a looong time ago, too long to give accurate details, but I can tell you the points I remember. I think it came on suddenly, like one day I was my usual self and the next day I felt distinctly odd. I had no idea what was happening, didn't know a name for it, but now I realize I had periods of anhedonia, or the inability to experience pleasure or joy, which was quite painful. Visually, things around me actually appeared to be covered with a gray film. I remember a numbness that was so deep it also was painful, though I know that sounds like a paradix. Time dragged, minutes taking hours, weeks passing by in years. Finally I had this brilliant idea that if I could feel physical pain, it would be better than feeling nothing and I took a razorblade and sliced through the veins on the back of my hand. It wasn't a suicide attempt, merely a desperate effort to feel something. And it worked to some degree. The dark-red blood running over my hand was the first real color I'd been able tp see in what felt like months, and the stinging pain of the cuts I definitely felt. It didn't dure the depression, but it did afford temporary relief. I don't remember now whether or how it affected my grades. I was a good student and may have remained so, though I can't imagine how. Over time I began to feel like my old self. Color returned to the world of ntural beauty in which I lived, time resumed its normal cadence, the numbness dissipated as did the anhedonia and I just thought that it was an odd experience in a life filled with odd things happening, given my chaotic family life and vivid imagination.
For the next year or so, things went on normally or what passed for normal in my family. Then when I was a junior in high school I began to "come out of my shell." I became much more social than I'd ever been in my life, though I wasn't a recluse before. Still, I interacted with other students more easily than I ever had, developed a wicked wit and a degree of (gasp!) popularity. I flirted with boys for the first time in my life and I felt pretty, confident and energetic. I was the editor of the school newspaper and tried out for the junior play--sommething very outside my normal self. Though I didn't get a starring role, my performance "stole the show" according to reviews in the local paper. I was unstoppable. Despite all this extracurricular activity, my grades didn't suffer because I had all this new energy. I thought I was merely coming into my own, turning into the kind of person I always wanted to be, but this, too, faded and by the second half of my senior year I was in a depression deeper than the one I'd experienced at 14.
While in college I developed a pattern: I was fairly "normal" in the fall, my usual studious self, but spring brought with it a restlessness that eventually turned into an inability to sleep, loss of appetite and loss of focus. By the time I arrived home for summer break, I was noticeably underweight and exhausted. Worst of all, there was always a great gap between my fall semester GPA and the one in the spring semester; fall semester I usually pulled a 3.5 or bette, while my spring semester grades were usually 2.5 or lower.
As I entered my 20s my "normal" times got shorter and the mood swings became wider, more intense. It never occurred to me that the way I experienced life was unusual and I didn't enter therapy until my mid-20s during a particularly deep and persistent depression. I was diagnosed with situational depression stemming from my first divorce. Two therapists and numerous 72-hour holds later, I finally underwent a psychiatric evaluation, was diagnosed with bipolar disorder, type I and began treatment. As the medication began to take effect, I knew the first sense of real peace since I was 14. I was 30 at the time of my diagnosis and beginning of treatment and lierally lost most of a decade of my life to mental illness. Though I was bright and capable of accomplishments, the mood swings were sufficiently disruptive to preclude the continuity I needed in order to finish any major projects.
That was my early experience with mood disorder. Sorry it's so long, but it's a complex, often confusing condition, difficult to explain and equally difficult to diagnose, though diagnoses are being made now in younger people. which is a good thing, I think.
To tell you the truth, I want to learn more because I'm a little concerned...I've been having more trouble with mood regulations. It might be simply because of stress or something, but I want to be educated just in case. 
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