After picking my hero in the pre-game lobby, I typically Alt-Tab out of the game to browse the web for a short time until the match starts. This time, when I Alt-Tabbed back into the game, my HUD completely disappeared! I could still control my character but I could not see my health, ult charge, ammo reserves, aiming reticle, nothing! In hero select for the next round, I could not see any heroes to choose from, so I had to stay with the hero I picked from the last round.
When I restarted Overwatch, my HUD was back on.
Why did my HUD disappear? How can I get it back if this happens again?