Life is great, so why do I want to kill myself?

I was really depressed a few months back. It made sense to want to kill myself then. Recently, however, I have felt a lot better. I even enjoy life, enjoy my relationships, and enjoy my work and studies. Life has flavor, life has fun, and yet, not every day, but often, the thoughts of suicide come back like a mosquito buzzing at the back of my head. It seems so attractive; thinking about ways to pull it off gives me a feeling I like. I forget about it or think it’s gone for good whenever something unusual, distracting is going on, but as soon as life falls into a routine, it’s back.
This contradiction makes me feel intensely guilty. Suicidal Ideation while you’re horrifically depressed is one thing, I tell myself, but while you’re happy? Surely that’s selfish and perverse! If any other person in the world said what I’m saying, I’d want to comfort them and help them, but this is me, and I only feel disgusted with myself.
I will not kill myself, no matter how much I want to. I have been taught to believe that it is wrong, and there are too many people whom I love who would be hurt. Nevertheless, despite this knowledge, despite my health and youth and friends and family and promising future, despite all the reasons that I should be totally ok, these thoughts continue. I do not know what to do. Please tell me that there is someone who has felt the same before!