On my Ubuntu 15.10 PC, Unity sometimes hangs. It happens quite seldom, but I have no idea what to do when it does. Additional info: 1) The mouse pointer is moving as if everything is OK, but clicks do not affect the UI. 2) The terminal session won't open with Ctrl-Alt-F1.
UPD 1. Just found out that the keyboard is not active at all when Unity freezes (all indicators are disabled).
UPD 2. That's a desktop computer. Tell me if you need other specifications.