i haven't had it done, so couldn't say. but my mum has had many similar procedures for her heart condition, many involving catheters in the main arteries. She has always said that they have never been as bad as she was expecting, and as you said, the benefits are worth the discomfort.
The worse thing was when they removed the catheter from her groin, but they explained what was going to happen and geve her some morphine . She was a high as a kite, and giggled all the way through. She couldn't even remember them doing it afterwards!
Hope that's helped a bit.
And, no, you're not a coward!
Whenever i have had to have something done, I remind myself that some poor child is probably having the same procedure somewhere.
If they can do it - I can do it.
good luck x x