I used to feel like this when travelling with my mum before she passed. The main things I did was ensure we always had really good travel insurance, even if travelling in an EU country, as it just gave us more choice about where she could be seem. Finding out where nearest hospitals were and how we'd get there as well. Finding out where best cardiology facilities were nearby (her issues were heart) and basically being as prepared I could be for anything that might crop up. Oh and taking copies of any prescruptions, carrying medication in hand luggage etc. Health issues can crop up anywhere and anytime, but the key thing I found helpful was making sure I knew where and how to access the type of help she might be likely to need.
Oh and also checking there were easy routes home should we need them. This meant driving to Europe during Covid so we could always get home rather than worrying about next available flights.
Bear in mind though that my mum was in her 80s with lots of complex medical conditions so I probably did more than was necessary but it did help me relax a bit about going. Plus it had got to the point with her where she was saying, I really want to go and I'm more likely to regret not going if I spend the week at home and am totally fine. So I guess also have a think about how you'd feel if you'd cancelled again.