I went to the Tower after smoking some Dregs in the Cosmodrome and noticed that my HUD had disappeared. I tried logging out and back in, but the problem remained. I then spent a minute or two in the Crucible and still had the same problem. (Control is impossible to play if you can't see which zones are being contested.)

So I closed out of the game completely and came back after a few minutes, which solved the problem. This was on Xbox 360.