Oh OP, you must be very scared - I've been there and I wanted to tell you my experience because I felt so very alone when we went through my (now) DH's illness. When he was 35 he had pains in his stomach and then started being sick, he had other symptoms too but failed to tell me them at the time. To cut a very long story short, he had a bowel disorder and had caught a hospital infection.
When he first went into hospital it went very slowly, endless tests and moved between HDU and ICU. Some days he'd improve then the next he'd be down again, one day he suddenly took a turn for the worst which was when they operated. The thing that scared me the most, but was the thing that saved his life, was the moving him between places - HDU meant that he was monitored so closely that if anything was to change it'd be noticed immediately. ICU meant that if he got worse there was everything there to help him, this was needed a few times. He made a full recovery, and I promise that things looked very, very bleak for him.
He's had a few operations since as he chose to have reconstructive surgery. Each surgery he's had has taken him to HDU, sometimes to ICU and sometimes backwards and forwards. In fact, the normal hospital wards are odd to us. He has come out every time, he's healthy and we no longer fear being told he has to go to HDU or ICU. But I always remember the first time, I thought I was going to be sick and felt a panic like I've never felt before.
My DH is now 35, he was 31 when he got ill so it's fairly recent. Please remember that hospitals, HDU, ICU and tests don't have to mean the worst, they all mean that he has a fighting chance, otherwise they wouldn't do any of that. It's so hard to put your faith in the medical profession but they saved my husband and for that I will always have faith in them.
I hope your DH is on the mend soon and that they can start to treat him soon. Please look after yourself, I wasn't pregnant when we went through this and it was very, very hard. I agree with the PP who suggested getting off the ward for some of the time, take a book with you to give your brain a break from thinking about the illness and about the tests and outcomes. Look after yourself and keep eating and drinking.
Feel free to PM me, I truly do understand some of what you are going through. My DH had an issue with his bowel and we've had some tough choices to make, it can be so overwhelming. But it does get better, my DH is fit and back to health. Very un-mumsnet-ty hugs to you.