Help Sony Xperia Z problems

[Android Question]

I've had this phone for quite a while, and had it upgraded to Lollipop recently.
Out of nowhere, it literally did sudden death on me when it was almost out of battery. I've tried charging, there is no light and only 3 flashes when I try to power on.

Should I panic right now?

 

[Slug]

Should I panic right now?

Not just yet.

Hold down POWER + VOL_UP (at the same time) for a few seconds. If the phone reboots now, you're good.

If it doesn't reboot, does it at least vibrate briefly when you try to power it on?