Hi Roseneath,
Totally understand all your feelings - helplessness as to how and when you will feel good or bad, and the fear that this will be the time that you just can't cope.
I know when we feel bad that it's hard to imagine ever feeling better, but you will! It is a blip, maybe triggered by things going on in your life, maybe not. As others have said, use any coping strategies you can, hang on in there, and this will pass.
Xx