iPhone 5 Frequently Crashes to Apple Logo and Screen Lock

I have an iPhone 5 64 GB running iOS 6.1.4 on AT&T.

Over the past ~ three days, have noted that the iPhone randomly "crashes". Could be when I am using an app. Could be when I am making a phone call. Could be when it is simply connected to the power cord and haven't touched it at all.

The cycle is as follows:

Screen suddenly goes blank

The white Apple logo (which typicaly appears during boot-up) appears for 3 - 5 seconds

I hear the "chirp" that normally sounds at the end of boot-up

The iPhone lock lock screen then appears

Sometimes, when the phone emerges from lock screen, the brightness is about half of what it was prior.

I have not been able to isolate this behavior to a specific set of circumstances. When it occurs during a phone call, the call is interrupted / other party is silenced, but if I swipe at lock screen, the call resumes (the other party notes that I went silent during duration).

I have re-started / re-booted the iPhone 15 times. I have cleared all apps from the cache. I have disabled all notifications and location services. I have done a Reset All Settings on iPhone and restored from iCloud. I have done a Restore from iTunes. The problem continues.

I would say that this crash cycle occurs about every 30 - 60 minutes. As noted, many times when I'm not even touching / using the iPhone.

Have also noted that when not connected to power supply, the iPhone is quite warm, and battery drain is at an accelerated rate of 3x to 4x of "normal", worse than prior iOS 6 related battery issues. Have also tried all the usual battery saving tricks - wifi is off, GPS is off, EQ is off, etc.

Any thoughts before I head to the Genius Bar?

Thanks!

TCF