You can tell the lab team how much you want to be sedated. I had one prior to my valve surgery in 2011. Had a bit of a glitch that time. I was supposed to be sedated, but I was still aware, semi-awake. When they inserted the catheter into the artery in my groin, my whole body tensed and I literally "bounced off the table." No pain, just wierd sensation. They put me out then, but I kept waking up during the procedure. Every time I would wake, I would look around at the screens, but then some doc would say "Uh oh. Time to go back to sleep." When I had a second procedure prior to having a pacemaker lead replaced in 2016, I told them of my prior experience. They were able to keep me out, so all I did was take a nap and they were done.
As for them finding a blocked artery, wouldn't you rather they find it now, rather than having it show up after valve surgery and having to do it all over again? When planning my procedure prior to my valve replacement, my surgeon told the cath team not to stent anything they found, but to ensure that it was in their report to him. They found one artery blocked 50%. Not a biggie at all, but he did a single bypass "as long as he was in there."