You need to ride fixed. If you're going to go through the trouble of converting an old road bike, you need to at least make it worth your while. If you can't stand it (won't be the case..), you can just thread on a freewheel.

If you get a flip-flop hub, you can keep a smaller cog (or freewheel) on the other side and flip the wheel if you need to "recover." I admittedly don't know anything about proper road bike riding technique and have no idea what a "recovery day" is. I just ride my bike. If I'm tired, I ride less or take it easy. I don't have any problems.