Patrick take a deep breath and calm down - I know that's really hard because I had a similar situation last year when my 8 month old grandson was rushed to hospital with septicaemia and it was touch and go he would pull through, but he did. It was the worst five days of my life and I didn't know it was possible to cry so much.
Babies are tougher than they look and the fact he was healthy and thriving before this is a very good sign - I'm sure the doctors will do all they can for him, it's really marvellous how paediatric care has improved massively in the past decade. My positive thoughts and wishes are with you, your family and your little baby cousin who, by the way, is absolutely adorable. I'm sure you'll be cuddling him and playing with him again very soon