Vanessa...
All CF's go through depression, some WAY bad depression. Here is the thing. Life by itself is very depressing. Add life + hardcore terminal illness/crappy quality of life CF to the mix, and it's enough to cripple most people. And we are people before we are anything else...
I was so freaked out when i was around 14, due to my mental instability at that time, I told my mom "Mom, either I get help, or I kill myself/and or someone else". She took me to the local psych elves, and I was institutionalized. I was in there with some REAL crazy freaks. It took 2 sessions of group therapy with some EXTREMELY OUT THERE people, to realize I was just a person with a healthy mind, that was in a crappy life with this bad disease, and I was losing it. I started doing self analyzation, and general deep thinking. It took a while, but by the time I was around 20 or 21 all of the depression stuff generally went away. I tried Prozac once, but it made me mentally feel like I was watching static snow on the TV. I quit that, and came to the conclusion that (as I said before), regular "normal" healthy life is hard enough, and filled with tons of things that can depress you. Throw in the aspect of having a disease where it's a constant struggle in every way just to survive and try to have some comfortable quality of life...And well, it's totally understandable why CF's are so freaked out.
Here is what I do/think to not lose it: Even though we all know CF sucks way bad, and we will die young, there is *ALWAYS* something way worse out there than having CF and dieing at our generalized life expectancy. While my lungs slowly get eroded away, my other friend has MD and in the small time I have been close to him, he went from being able to fully take care of himself, to having others have to move his limbs for him. Look at poor parkinson patients. Imagine shaking worse and worse over time till you die before long. I mean there are countless worse diseases than we have. Atleast we can get by for a while with some semblance of positive experiences (we can do a ton of things, even if we are severe) while we are here.
I am not belittling your problem if you go beyond the same mental aspects we all have dealt with. If you have VERY serious depression aspects, seek professional help in every way. My advice is advised for those who are like most of us, and let the negative aspects of being alive with CF overwhelm them.