My opinion is you have a couple of options, and both may need to consider other explanations than your pre existing cardio vascular condition. Firstly would be an urgent appointment with your GP, ie immediate not waiting, or walk in to A&E. The body is a complex system and your heart condition can be a symptom not just a response to other symptoms. You are clearly anxious and know what is normal for you. The cardio nurses expertise may not be what's required to sort this out.
Such a low blood pressure could be giving you the symptoms. It’s a long wait until Monday when it’s so low I agree you need seeing sooner. I’d ring my gp.
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