Depression

I'm ceasing to function as a normal human, as some one who I once was and recognised. I'm no longer happy or able to enjoy myself. I've turned into this person who is sad all the time, wants to cry but doesnt want people to know how I associate nearly everything with something sad or depressing, wants to help people but is afraid of pulling them down. Is this depression I'm suffering or is it part of the cycle? The horrible aftermath or the terifying begining.
A few friends have noticed how I'm feeling and asked if I'm ok but my answer is always "Yes" while I know I should say "I will be eventually" and I'm screaming inside "No!". Why can't I tell them the truth? I know why, because I want to protect them, protect them from the horrible truth, and I don't want to drag them down with me.
I know I should tell people, see a counsellor or a doctor or something, but I can't That would involve admitting that I may really have a problem and that's something I can't deal with. Better to suffer in silence with my pain and my hurt and my tears