oh have a hug! For a while I was unable to pick up the post - I was a great letter writer but couldn't reply, so if a letter from a pen-pal arrived I would feel really ill - because I felt I had to reply immediately

: I was unable to answer the phone; I couldn't answer the front door, have people to visit, go to see anyone ……. fear is very controlling, allowing the mind to keep going round and round ……… it is a vicious circle, self perpetuating.
How about a community psychiatric nurse to visit so that you can talk these issues through? Your GP could arrange for this. Or get in touch with the MIND charity, they may have an out-worker who could visit with you. Being in your home may allow you to feel relaxed, more in control. Or perhaps you could have a correspondence about your worries with a professional? Making a list and ask the Nurse to go through them with you even if it means several discussions? That way what is in the back of your mind can come forward - talking about it can help.
The blood tests you are having won't show anything untoward health wise, because they are different types of tests. Speaking with your Practice Nurse could help or a Pharmacist. If a Nurse explains the various tests for different symptoms you might feel easier about what 'might' show up.
Thyroid disorder can cause anxiety. As can low blood sugar. Do you have a 'good' diet?
Keep posting!