The Cavalier King Charles Spaniels are super dogs! Lots of personality and very sweet natured.
I do understand your fear and it was one that I worked through myself. My dog, a Bedlington Terrier, has a predisposition to liver disease. But I never focus on that anymore.
If you get a pedigree, then you should be able to check the history of the parents and those before them. A predisposition is not really the best indicator of future health because they don't take into account what a dog is fed, vaccinated, neutered, or how much it is loved. There are so many variables.
Being a dog carer, you have so much more control over its health than the health of a child, who will eventually grow up and leave home.
Of course, it's important to have pet insurance for emergencies.
Fear is very crippling. It can stop us doing amazing things or having the experience of something totally wonderful because we fear something that may or may not happen. To move away from that means we must live in the 'Now'. The Peace of Now, moment to moment. In each moment, there is no pain. Just 'What Is'
And the fear is never as bad as the actualisation, because when something does happen, a clear mind knows what action to take.
And what is the worse that could happen? A dog gets sick. Yes, it could happen. It can happen to any thing or any one we care for. The worse that could happen is you become even more compassionate, more loving, more caring, more giving, more everything - and isn't that what we are here to learn to be?
To live is to love and be loved unconditionally. I don't know if there is any other purpose for us but to remember that - and that is the way home. And all love, whether short lived or long lived is eternal. Because love never dies. Love takes us home.
And any opportunity to love unconditionally and be loved unconditionally is such sweet ecstasy. It's something I get to experience every day. I look at my dog, he looks at me. A connection. Tail wags. Shivers down my spine. It's a simple act, but these are the moments I feel most happy to experience. Because it's something so pure and honest.