Yaris wont start/dead then started working again

[nugget]

Hi guys,

Really hope someone can shine some light on this issues, I have felt my 2011 Yaris is very reliable, up until today.
Keyless, petrol version with automatic transmission

After work, I got to my Yaris and the keyless system opened the door as per usual, I got in and pressed the start button. The dash went on and then suddently everything went dark. Nothing happened. The car was completely dead.
I tried using the buttons on the key, jerking the automatic gear which was stuck on drive, pressing the start button with the break applied. Nothing happened. It didn´t respond to anything I did.

Baffled I opened the driver door and when I did, everything went back on again. I checked the dash and it was bright and clear (not a weak battery) and put the gear into normal and pressed start. Everything worked and I had a somewhat worriedsome journy back to the house.
The clock and my selected radiostation was defaulted, but apart from that, everything seemes fine now.
I tried starting, stopping, locking the car and all sorts of stuff when I got back, but no problem.

Does anyone know this could have been. A one time glitch or something I need to check out? Basically, should I be worried?