To a critically ill patient, an organ transplant means a new start, a second chance. 

But the body is designed to fight off any outside invader. Even one that's trying to save it.

 Because a transplant doesn't guarantee that it's an easier life. There's a threat that the body will reject the organ outright. The transplant process is very scary. A patient goes from worrying about getting an organ to worrying if the organ will be rejected. 

The anxiety continues until they can finally open their eyes after surgery and see that their gift has been accepted.