I've never been diagnosed with depression, and don't know if the underlying sadness I've felt for so long can be attributed to that. Depression "runs in my family." I'd say generally I'm happy, there's just that nagging feeling that resurfaces whenever (usually) I'm alone/not busy.
Recently, I've begun feeling these rather sudden feelings of hopelessness and apathy... additionally, they most often happen at night as I'm falling asleep, or if I wake up in the middle of the night. Sometimes they happen like a bad dream as I'm drifting between awake and asleep. Often, these feelings are accompanied with feelings (yes, feelings, not really cogent mentalese thoughts) of "I can't believe I exist... I can't believe this is what I'm doing with my life...What's the point? ... Do I care anymore if my life is cut short?" Not that I'm particularly contemplating suicide.
Is this something I need to worry about? Or should I just keep doing what I'm doing: trying to get more exercise, trying to stay busy, involving myself in various mental pursuits?