Depression

Depression is quiet, anyone can fall victim to it, and people usually hide it using a smile as a mask and an 'I'm fine' as persona. It is because hiding it is so easy that oftentimes only you will know of it, and the cheerier you are the less they suspect, but it is sometimes the ones with the cheerier outlook with the deepest depression. But everyone has a breaking point and you can't hide it forever, so eventually someone will find out. But don't be ashamed because there are people around you that understand and who love and care about you. It is by talking to those people that you can gain the courage and confidence to overcome this.
Most importantly remember that you are loved, you are appreciated, and most importantly you are not alone. It is a great big world out there and sometimes it is hard not to get lost or detached, so keep in mind that the ones who care for you are and will always be for you.
You are not alone in your struggle, and there are millions of other people, each unique in there reasons and each going through the same mental turmoil,  and it is often the ones who have overcame this struggle that will be there to help you find yourself and beat your demons.

I speak as an outsider but I have friends who go through this too and I will do nothing but help as best I can. I've done it before and I'll do it again. So stay strong and you'll come out as the beautifully perfect, unique individual that you are and remember that those who love and care for you will be with you the whole journey