To say that you don't necessarily look sad all the time, or even any of the time, even when inside you are screaming.
To say that one minute you might be laughing with everyone else and the next be sneaking off into a corner to shed a tear or two; this may happen up to and including a gazillion times a day.
To say that you might find yourself switching between feeling invisible and needing attention, and feeling like a rabbit in headlights because people are actually looking at you and you think they probably hate you because, well, why wouldn't they?
To say that you do want to make and keep more friends, but contacting anyone and putting yourself out there feels like standing on the edge of a cliff.
To say that it isn't actually as simple as getting out more/pulling yourself together/a cup of tea/a good cry/cheering up, etc.
To say that you aren't standoffish or rude, you just can't open up to them because they might hurt you.
To say that laziness is not the same as being so totally overwhelmed by your own horrible brain that you are glued to wherever you stand or sit and can do nothing but stare into space.
To say that even though you don't open up to people (see above) you still might desperately want somebody to understand you and maybe even give you a hug.
To say that you might find something terrifying, like leaving your own front door, even if you've done it a million times before, and you might not even be able to figure out why it's so scary.
To say that you might take things really personally even when everyone else can brush it off.
To say that you might answer "I'm ok" when somebody asks how you are, even somebody close to you, even when you really aren't. It's not lying, you just say it automatically because you are caught off guard.
To say that you might not let your feelings out until far too late in the day (literally or metaphorically), you aren't doing it to be annoying, you just couldn't manage it earlier.
To say that you might appear really happy and proud of yourself and confident sometimes, but probably inside you still can't stand yourself.