The way it works right now, you will gain fatigue slowly throughout the day. If you do nothing about it, that fatigue will overwhelm you and you'll literally pass out wherever you are and sleep until you recover enough to stand back up. You remove the most fatigue, most quickly, while sleeping -- it's definitely the best way to get back to 0 fatigue... but, it's not the only way, either. You can also rest by a fire, sit in a chair or on a bench, or partake in a few other relaxing actions that will remove some of your fatigue. it will happen more slowly, no question, but it will work.
Essentially, you will be able to take shorter, more frequent breaks to mitigate fatigue if that's your strategy, as long as the ability to rest is actually possible wherever you are, which isn't guaranteed unless you bring the tools to make it possible yourself.
Hope that helps! :)