Something similar ....
I had a similar experience on the 15th .... took my N5 off the Qi charger and the screen froze when i tried to unlock it.
I hit the power button and was able to unlock and get a few touches in before it froze again.
I was finally able (after much screen off/on cycles) to get down to the developer options and turn on show touches & show cpu usage.
... background processes looked fairly normal when the screen was frozen(touches showed as frozen) ...
I was rooted, stock rom except for xda user Jishnu Sur's N5 camera mod and running a couple tried & true root apps(Stickmount & QuickBoot). Thought some software issue might be jamming up the digitizer i/o causing it to freeze.
Reverted entirely to stock (the Team Win recovery was also experiencing screen freeze - buttons worked fine) including removing TRWP and re-locking the boot loader!!
The screen freezing problem persists ... my conclusion is that it's a hardware issue.
It's possible you are seeing the same thing, but I haven't seen anything in the forums to indicate it's a widespread problem.
Returning it for a replacement phone ...