Welcome Phil,
I have had - and probably will have again in the future - the same experience of anticipatory anxiety. I also understand how the original stressor can be overtaken by the intense physical reactions of the body/mind, ie. the constant state of arousal, feelings of anxiety and fear, and bouts of poor sleep. What I would like to remember when in this awful place myself is that I'm still a valuable person in the midst of all this tumult and that I deserve care and support. Support from others has been important for me in times of real distress. This can be a close family member, a friend, a counsellor or a helpline. Help comes in lots of forms, consider which kind of support feels easiest to access at this time. A first step is a good step.
I now realise that I also can be a much better support/advocate for myself too. It is probably an important part of the healing journey to learn to be your own reliable friend who is "on your own side" in tough times. Can you extend some compassion toward yourself knowing how hard this experience is for you? I am still at the start of my journey toward self-compassion and yet I have glimpses of its capacity to reduce my feelings of self-blame when I'm suffering.
Much of my anxieties have a link to insecurities in my relationships. Working on being more honest and assertive is the long-haul work of reducing the anxiety sparked by fears of rejection and abondonment for me. This is sometimes difficult work and does require others to work with me as i renegotiate how I want to be in relationships. Today, after some time spent on this, I can say that things are changing in positive ways for me, and I feel more real - and sometimes more awkward - when with others.
My main suggestion for now - be as gentle as you can with yourself and reach out to another for support.
