Did I run out of battery or hit the reset button

I had stopped with my Nuvi 260 in my pocket for 3 to 4 hours. When I returned to the car and put the unit on the mount I had lost all of my favorites, Only the Garmin locations for USA, Europe, and Canada appeared in favorites. It also asked me to register the unit. Luckly the unit had the hotel we were traveling to in its POI index. I saw on another posting that removal of their units battery did not cause loss of the favorites. My unit battery is not removal, but internal.

I did learn from this that I should slide the on/off lever to the lock position after turning it off to prevent future occurances of batter loss.

So was it battery loss or reset by accident? Any guess?