Here's what depression isn't:-
It's not just feeling a bit down, or miserable, or sad, or unhappy. It isn't a temporary thing that lasts just a few hours or days.
You can't just 'pull yourself together', or 'snap out of it'. You can't just switch yourself on and off - there isn't a switch.
Things won't 'look better in the morning, when you've had a good sleep' (sleep is often impossible when you're depressed). Nor will watching a funny film or doing something you like or someone telling you a joke make you feel better (you have no feelings when you're depressed, and humour or even sarcasm go right over your head).
And what depression is:-
Knowing that people around you simply do not understand, especially if they've never suffered with depression themselves.
Feeling emotionless, frozen even.
Not caring about anything, even yourself.
Getting through the day and doing the normal everyday things that need to be done, by a sort of robotic action - just doing it, without really even thinking about it. And then finding at some point that you've done something like getting a bag of peas out of the freezer for dinner, and put them back in the fridge instead of the freezer, and having no memory of doing that. Or gone to check your bank balance online, only for your mind to go totally blank and you simply cannot remember your log in details. Or go to take your BP tablet which you forgot to take earlier, only to find that you've already taken today's but forgot to take yesterday's (it's a calendar pack so I know).
Having someone talk to you, then realise that they've stopped talking and are looking at you expectantly saying "well, what do you think?" and you realise they've just asked you a question and you have absolutely no idea what they've been talking about, you haven't heard a word they said.
Being unable to raise any interest in anything, and not even care that you can't. Also being unable to make a decision, even a simple one like whether you want a coffee or tea.
Not wanting to do anything or go anywhere and when someone asks you why, you just shrug and reply "I can't be bothered" or "I don't want to" - just a bald statement that you can't be arsed to pretty up or explain.
I WILL get through this, it WILL pass, I know that. But until it does pass, I'm just going with the flow. And others will just have to accept that.