Desperate to get rid of phobia: listener question

 I'm struggling with my phobic reaction around health checks, specifically blood pressure.  

I have my pre op screening on the 31st Oct and was just looking at the appointment letter to see what was involved.  I had a reaction which I can only describe as a full blown anxiety attack.  The adrenal rush was huge, my heart rate went into overdrive and god only knows where my blood pressure is. Tunnel vision, dizzy, the works.  Two hours later I am still suffering from the after-effects....feeling really toxic.

When I sit with this I'm only seeing the after effects of something that happens in a split second.  I feel like it's too late by the time I have the opportunity to sit with it.  I know it's only thought and feelings, and neither of them are really me, but it's truly awful.   It's the biggest double bind.  The anxiety which causes my blood pressure to spike is caused by my thoughts of having to have my blood pressure tested.  It's about getting awful news I think.  In this case it is self fulfilling in a major way.

Do you have any thoughts on what I can do?  I somehow need to break the link between the trigger and the response.

I'm getting a bit desperate.  I think they will cancel the op if the blood pressure is too high.