IT happened to me too! On my 4S, while driving through Baltimore using MAPS. It just suddenly blacked out, and I tap the home button thinking it had hustled faded out. When it stayed black, I thought it was dead and started to panic since I was in unfamiliar territory. Suddenly the Bluetooth told me to turn left. So it was really ON! Siri also worked when I checked it. I brought it in to Apple and they said the screen had just gone bad but the battery was all right. I brought it into another Apple store and they said the battery had overheated, and the whole phone would need to be replaced. I felt the cost was too much so I upgraded to a new phone. But I always wondered what really happened because this happened right after I upgraded to iOS 9.0.1