I've had long spells of 'low mood' for a good few years. For ages, I wanted to know 'why'. My life is good. My wife truly loves me (I've stopped wondering why - no good can come of pulling on a thread!) I have a good job and am well-off financially.
It wasn't until recently that I realised that knowing 'why' doesn't really help. I discovered that I have low testosterone. That causes (amongst other things) low mood. Having T treatment helped my mood enormously, though the levels do vary a lot - so often, low mood returns.
When it does, life seems as hopeless as ever - even though I know 'why'. But I've realised that it's still 'me' underneath the fog. My values are still the same, no matter how I feel or how temporarily grouchy I might be sometimes. When I can keep that in mind - 'I'm not the feeling. I'm not the thought. The moods pass and 'I'm' still here' - it's much more tolerable. I just have to remember I'm still me!
A Moodscope member.