I use a heuristic for cases like this: What did ~11th century Catholics do?
Crusade to retake the holy lands. Sounds tiring. I recommend you stick to the gardening idea for rest and relaxation. Or, at least, stick to the heuristic "What would Will's fantasy model of an 11th century Caotholic do?"
Invading to take back lands that were taken from you or your allies by a hostile power is something that even 20th century westerners do.
So, it's well-known (or, at least, oft-thought) that you can't just work 16 hours a day; if you want to get stuff done, you need to rest from time to time. You have to take breaks.
Today, just now, I realized that I don't really know what the best way to rest is. If I want to rest, should I do something that's fun and interesting, like reading a fantasy novel? Should I do something that's boring, like building roads in Minecraft, so that work will seem comparatively interesting when I get back? (And besides, reading a fantasy novel is a bit of a challenge, at least for me, whereas building roads in Minecraft is trivial.) Physical activity probably helps, but how much? Do relaxing activities, like taking a warm shower, help more than just sitting there? How can I tell when it's time to take a break? How can I tell when it's time to get back to work?
(Suggestions for tags would be appreciated.)