What do you do when you feel yourself slip into the darkest corners of your mind?

When you don't have the energy or the heart to talk to those you love because you're afraid of hurting them or them now understanding. How do you explain why you're sad when everything in your life seems to be okay?

How do you tell them that every now and then you have an extreme urge to cut a slit in your skin so that you feel some sort of relief. How do you explain that they are the reason that you haven't hurt yourself but you don't know how long this will go on for?