I actually had this problem last night. My battery was at 20% a few days ago... left it idle, went to use it last night and bam, nothing.
Plugged it in for a few minutes and tried to boot, nothing. Left it for about 5 minutes and then just held down the power button until something happened, and finally I managed to get the battery icon to appear. It would stay for a few seconds then the screen would go black. Then it would return. Rinse, repeat. I couldn't even get it to stop doing that. Eventually gave up and just let it charge for another 10 minutes.
Looked at it after that and it was booted. Battery page shows it dropped from 20% to completely dead instantly. Not sure what's up with that.
The whole time I was doing this procedure, the notification light was pulsing in sequences of 5, if that means anything to anyone.
Anyway, tablet is fine this morning.