What is depression?

Depression might never be visible to others that only see your happy Social Media. 
Depression can be coming back home and marching straight to bed, never wanting to get up again. 
It can be tears streaming down your face while you go food-shopping. 
It can be getting up in the morning, thinking about how glad you will be when you can sleep again.
It can be not being able to get past the entrance hall of your house, slumping down on the carpet, unable to get up for hours, with just your dog's astonished toys watching, nobody else knowing how you feel when you walk out the next day again, smiling to everyone.