Do you know when you are just down and when you are actualy depressed?

Like some here have said. It's a situational judgment. If you are sad, but for a legitimate reason and in proportion to the situation, that's "normal".

When you have those kinds of feelings for no reason, or extremely out of proportion to the situation, you may have a problem. That can include weeping, fatigue, a feeling of hopelessness, and a thought pattern that includes considering suicide as a legitimate solution to your problems.

If you are at the weeping/suicide stage, please seek help. It will amaze you how much better life can really be if you get treatment.

If you feel sad, negative, anxious, concerned, pestimistic, discontent, ... & so on
To feel like want to express out by crying but you cant !
To find out the causes of this feeling but no answer ! That's DEPRESSION which is the sign that leads to
MANIC DISORDER --> BIPOLAR DISORDER !

Usually when you are just feeling down it does not last and there is a specific reason for feeling this way. Being depressed you feel hopeless day after day sometimes you don't even know why. Sleeping patterns can change and also eating habits. Your actual quality of life is affected.

when im down i just feel kind of blah and when im really depressed ill stay in bed or cry.

i know i'm depressed when i really, really find it ahrd to concentrate, when i'm too irritable, and when all i wanna do is sleep. also when i feel so hollow.

Yea, I think I can usually tell the difference. When I'm just feeling down or having a bad day, it's usually triggered by something I can pinpoint. Sometimes it's just that little things build up until it's simply too much, and I hang my head in defeat. Sometimes it's just the weather.
With a depressive episode, the feeling of hopelessness and extreme sadness is just overwhelming. You can't will your way through it. For me, there's no particular reason for it. But that's what clinical depression is. In a way, it's just that you're sick. If you're unable to feel happiness for so long that you forget what it feels like, there's a good chance you're not just bummed out about bad circumstances.
People get the two confused a lot, and I think it's really screwing up society.

You may not be able to tell, but others can. All that everyone said in the other comments are true symptoms of depression. If you recognize any of those, get some help. Medication can make a world of difference in those symptoms and how you feel. In my case I did not realize it but others did and they got me into therapy. 5 months later I was better and have improved ever since.