Feeling sad for no reason

For years I have felt sad without knowing the reason.  Some nights, I'd feel very bad.  A feeling of missing something essential, though I wouldn't be able to pinpoint a thing that I miss.  I'd sometimes discover something as the cause for my worries.  Once such a discovery has happened, I can then consciously think about that and worry deeply.  It has never helped much.

Only a few weeks ago I found out that I don't know the reason for my worries because there's no real reason.  Because I was never worried.  I was only feeling tired and/or sleepy.  Just letting myself relax and rest would bring my happiness back.  Mind is a wretched thing that rejoices in its own tears!