well you lay around in bed all day, don't want to move, are to move, feels like something weighing you down. Have a one track mind and focusing on all the negative things in life. Hopeless. Cry with out warning and don't know why. Isolate yourself from other people, don't want to be bothered. Want to be alone. Some times don't want to eat, or over eat.
Lose interest in the things you enjoy doing, or like doing.
There is a whole list of things! When life becomes overwhelming, and you stop doing things, and just don't feel good at all. It feels heavy and like weight is on your shoulders, or like a dog in a cage that can't get out. You have to many thoughts racing through your head.
You might not know right away you have a problem. When I was 23 didn't realise I had depression or that was the problem. Your whole life just gets messed up with school, work, relationships, everything around you. It's been along time but these are the things I remember.