I had my knee replaced 6 months ago under an epidural. Brilliant, no pain whatsoever and no after effects. I was drinking a cup of tea 15 min after the op and eating my dinner an hour later. I had my hip done under a general anesthetic, would always opt for epidural should I need to have other knee/hip done.
The anesthetist will be with you all through and give you any sedatives you may need (I did not have any sedatives and was totally awake, chatting to anesthetist and surgeon. But if you are worried they will sedate you.
I have had a few ops under a local, that was always uncomfortable, with an epidural there is not the slightest discomfort. Just look forward to a new knee.