bluetooth.service running, but bluetoothctl says "org.bluez.Error.NotReady"

Okay, wow, turns out all I had to do was run

bluetoothctl power on

I got the same problem. It turned that the @turf answer didn't work for me.

After I checked rfkill:

$ rfkill list
0: hci0: Bluetooth
        Soft blocked: yes
        Hard blocked: no
1: phy0: Wireless LAN
        Soft blocked: no
        Hard blocked: no

I ran the command:

rfkill unblock all

And the Bluetooth worked again.