I've not travelled outside the UK since 2013, but as I have MS I knew it was imperative to have travel insurance 'just in case'.
It's a good thing I took out the cover as within 36hrs of arriving in Turkey, I was admitted to hospital with MS related symptoms, and there I stayed until it was time to head back to the airport 5 days later.
The bill for my time in hospital was just over £23k (fully covered by my insurance), and I'd not had any major tests or treatments at all, it was basically a few standard blood tests, a couple of bags of fluids, a few tablets, a bed and food for a 5day stay.
I would also advise the OP (and anyone else thinking of booking a holiday) to get the insurance immediately/as soon as they book their holiday, because it will cover them if for some medical reason they are not able to travel, they will be able to claim for a lost holiday.