I've suffered with depression since being a teenager, but I didn't really know that or could put a name to it until in my 30s about 10 years ago.
Up until my awareness, I saw the problem as being the world outside me, so would leave jobs, courses, move home etc thinking that would fix things, but it didn't.
Then I bought a book 10 years ago 'Feeling Good the New Mood Therapy' by Dr David Burns and that was my 'light bulb moment' of seeing that I was actually very depressed and this was being caused by illogical thoughts and judging myself very harshly. So all the lack of motivation to do anything, feeling tired all the time, tearful, irritable, finding no joy in anything...It was depression.
So nowadays I have all the authors' books.
I now know the depression warning signs...usually for me: not finding anything enjoyable, no motivation to do anything.
I sit down for 10 mins/half hour/hour with my CBT books....
Firstly: I do the 'Burns Depression Checklist' test that are in the books (I photocopy it from the authors' 'Seven Days to Great Self Esteem' book as it is nearly A4 size already)
This is a very short test which gives you an accurate reading of how depressed you are.
Then I do the CBT exercises which I find work really well for me. 'Downward/vertical arrow technique' (to uncover hidden 'self-defeating beliefs' that are causing depression, such as: 'I have to be perfect', 'Only people who are loved can be happy' etc etc )
Cost-benefit Analysis of those beliefs/emotions etc, then write a new alternative more realistic belief .
'Acceptance Paradox' (from his later books, deal with thoughts like 'I'm defective/a loser' etc and then accept that yes I do have loads of faults etc and that is perfectly okay!) are my favorites.
Then I do the 'Depression Checklist' again to see if my score has improved....I can often go from very depressed to 'minimal/no depression' scores after one sitting, because I find the exercises so amazingly effective. If my score hasn't improved as much as I'd like, them I do more exercises and try to pinpoint anymore illogical thoughts hanging around that I haven't dealt with.
My mood has then lifted loads and I can then get on with doing stuff and can find joy in things again...start looking forward to stuff again, make plans etc...everything I don't do/want to do when I'm depressed.
And just because I slip back into depression after a few weeks/days, I know doesn't mean the treatment isn't working....depression is something that isn't magically cured forever...you still have the same mind that created the illogical thoughts in the first place, and so it can still create those thoughts again...but what I've found is the depression is now not 24hr/day 7days/week and when it does pop up a few times a week it is far less severe and, most importantly, I have the tools to deal with it...and I LOVE doing the exercises 