Power Shut off and would not start

Parked the vehicle, turned it off, even closed the sunroof and turned the radio on while we sat for 15 mins. All of a sudden the vehicle shut off completely like it normally does after about 15 mins. Went to start the vehicle after about 30 mins, the brake pedal wouldnt move, the push button start wouldnt push, there were no lights, not even the radio would work. Opened the door, no interior lights would work. Tried the key faub, nothing worked. I waited about 5 mins, kept trying to turn anything on, and then all of a sudden the power was restored, vehicle turned on like normal, everything worked, no codes popped up.... Any idea what caused it ?