Suddenly, my left event sidebar is gone, and I can't get it back. Is it something I clicked or is it a glitch? I'm freaking out.

If you look by the clock on the layout you should see a button called "Toggle Sidebar" you might have tapped or clicked that by mistake? If you click it again you should get your sidebar back.

I logged out and logged in and logged out and logged in about 4 times and on time 5, somehow, it worked. Go fish.