Now, iamspecial, please don't jump to conclusions here about your friend. She might be just not answering the phone because she is depressed. Or she may be in the hospital, a good place for someone who is very depressed as she must be, or you wouldn't be worried about her. But if something were to happen, it WOULD NOT BE YOUR FAULT! You are not responsible for her--she is. You are only responsible for yourself. Have a concern, yes, do keep trying to reach her, yes, but don't think the worst. It probably isn't the case. Why don't you take the time to write your friend a letter and tell her the things you'd like to...the things you cherish about her and your friendship. That would be a positive way to fill the time and think about your friend, rather than conjuring up images of the worst, occupy yourself with that.

And be kind to yourself--you deserve it, for caring about your friend!