Have you ever felt depressed for unknown reason?

I have been trying to figure out the cause of my mild depression recently but without success. The weather? Nope, it’s sunny here (though it is getting cooler than the previous days). Something wrong happening to me? Maybe, but I can’t think of anything really making me depressed. Pressure? Nononono, not under any particular pressure…

But it’s not really depression that I feel. It is… some kind of empty feeling. Something more like “I’m alone, in this world”, though I can’t really describe it with words. Something told me that it’s a normal thing that teenagers sometimes experience this “I’m sad, but I don’t know why” feeling, those I’m not sure.

Have you ever had any feeling like that?