I've got quite a peculiar problem with my Nexus 5.
Last night, I left my phone on charge. It was working normally and the software was functional etc. However, once I woke up, the phone was constantly restarting itself, and wouldn't load past the boot animation. I tried to load up fastboot to enter the TWRP recovery, however, the phone froze on the load screen. I should also add that my custom boot animation was replaced by the CyanogenMod mascot.
This problem has never occurred before, and I really haven't got a clue how to fix it. I tried to use WugFresh's NRT to flash a factory image of Android 6, however, the command terminal indicated that each process had failed. This did not restore the phone to its original condition.
I should also point out that I have been running a CM 12.1 nightly, which has been very stable and I have been using this nightly, without major problems (bar the infrequent system UI crashes) for a couple of months. It is obviously rooted and I have a Nandroid backup, which I can't access for aforementioned reasons.
Please could you help me with resurrecting my phone? I would be happy to clarify and elaborate upon any point of information.