I'm sorry you are feeling so low. Try to remember that the fog will lift - it always does. This is not a permanent feeling, even though it can feel like it is.
The fact that you asked T for some more time suggests you may actually want to tell her your thoughts, but may be scared - understandably so. But this is why T is there, to help guide you out of the fog. You can do this. It will not always feel this bad.