Astrasoul,
I so sorry that you feel so down...
Perhaps by asking that question you are already aware of the answer. Being Very Sad is a rotten feeling because life is meant to be enjoyed, not necessarily great all the time but at least having some joy in your heart.

Apart from the desire to hurt yourself or another, there are other signs to look for...by no means is this a complete list.
Appetite is either non existent or eating more than usual.
Loss of interest in activities you usually enjoy.
Sleep pattern different; wanting to sleep all the time or not being able to even when you are tired.
Thoughts not actually suicidal, but thinking the world might be a better place without you.
Pushing yourself to bathe, do daily chores, missing work/school...any number of things that are different from the way you usually are.

Is there someone you can talk to? Your physician?
Many times a short stay in the hospital stops the spiral down into depression.

Please keep posting and let us know how you are, ok?
We Care

Peace to you,
Cap