Have to chip in here, as I myself have had HA issues, although am over it now. Thank god. I know how all consuming they are. During my 2 years of having them I ended up having a scan to rule out ovarian cancer, a mammogram to rule out breast cancer, and a one of those tunnelly scans to rule out a brain tumour! Thank god I had private medical insurance so I wasn't wasting nhs money. Not that it is any excuse...but I feel v embarrassed looking back. It was only CBT that stopped the cycle, otherwise I'd still be in it now. I knew it was mental health issues deep down but I just couldn't convince myself. The anxiety actually triggered all the symptoms that lead to the scans. Anxiety caused IBS, I had the most god awful pelvic pains, pains in my thighs, couldn't bend over due to pain. It was all caused by tightening my muscles due to anxiety. I could never convince myself that it was me tensing my muscles, cause it's quite a subtle thing you are doing but it's a constant thing. When you are doing that all day and night, it is painful. I have no doubt you are doing something similar, not identical but similar and whilst you are having symptoms you can't relax, so those symptoms are not going anywhere for now.
The brain scan was because I had a raging headache for 3 weeks...again because I was tensing my head muscles and constant googling. I then noticed that one of my pupils seemed bigger than another, I think I had read this could be a tumour. My gp also could see a slight difference in pupil size, so he agreed to refer me privately. It sort of makes me laugh looking back, but also feel very ashamed too. Over the past 3 years the only reason I can remember going to the doctor is for a painful bunion. So I have come a long way!! I doubt my experience is going to convince you to just stop it, but I wish it would!!
PInk Frock's urges to tell to you to get a grip...is actually a very normal response and actually it isn't unhelpful to hear that. This is what all people, who don't have HA would tell you and actually what people who do have HA would probably tell you too. When I had it I used to read No More Panic and the reason, why it helped me, was how nuts everyone else sounded! I used to think...why can't she or he see, that they are fine..? They've had all these tests and they still can't let it drop? Then I'd think, I'm exactly like them...I'm fine but I just won't let myself live and be happy. I was only half a mum and half a wife during that period. It's blatantly obvious from all your posts that there is nothing physically wrong. Clearly, if you could just stop the worrying, theN you would. you have, by booking that scan condemned yourself to a whole Christmas and new year of anxiety, until you get seen.
You would be so much wiser investing that money into private counselling instead. Then maybe your family would have a happier Christmas too? Google private CBT local to you. Take control of what is happening to you and stay busy too.
Whenever I have time off from work and head space to think about anything at all, that's when I start getting the beginnings of HA back again. Fortunately, I am able to talk myself out of it more effectively now.
Btw, re. The black stool. I have also indulged myself in lots of still gazing in the past too. Honestly, it is pointless. Food colours your faeces every which way.
Good luck to you. Please listen to that inner sensible voice and not the crazy one.