Its impossible to know what happened exactly, but sometimes you will get one wonky zwave device that wreaks havoc and causes so much traffic it overloads the radio firmware until it locks up. The fix is to power it off for a minute and then boot up again. If it keeps happening then you try to narrow it down to what device it is and remove it or fix it by adjusting settings.
Same thing could happen with a Wifi router, takes a little more to overwhelm one but I have seen it happen. Same fix as well, unplug and reboot.
With the most current zwave radio firmware these issues have been greatly diminished. Double check you do not have the "Update Firmware" button available on your Zwave details page. If the button is there you have an update. These instructions are still good but the version they mention is not current anymore: C7 2.3.1 and Z-Wave Firmware 7.17.1
