I can totally understand what you're feeling. But, keep in mind that even a well-bred Cavalier can be faced with some serious health issues. Believe me...I know. I've been through a couple of health issues with my two, but we've addressed them, overcome them and moved on. That said, what can you do? Don't overreact or be overly sensitive. Since you are informed on health issues you will know if something needs addressing. Enjoy Mackie and live in the day. Wouldn't it be so sad to worry so much you don't enjoy him...and there's nothing wrong with him? Get regular check ups at your vet, sign up for annual health clinic if they're available to you but most of all, enjoy your boy. Feed him a good food, give him exercise and love him. That's all anyone can do.
Loving mom to Jake, Shelby and Micah