I have to recenter ED every time I start the game. As others have said, you can bind a key/button for recentering the HMD. Sometimes if I take the headset off to google something, or go AFK for a couple of minutes, I might come back and find the orientation hosed up again, and need to recenter. During the game, it all depends on whether the sensors lose sight of the headset when you put it down. But ED is pretty good at randomizing the orientation when the game starts, for some reason, so it's best to just get in the habit of recentering every single time.