2001 Grand Marquis GS starting problem
 

I have a 2001 Grand Marquis that is giving me some problems. I went out Saturday to do some errands, got in car and it started just fine. Drove to my destination with no problems. Went into store came out in less than 2 minutes and my car wouldn't start. It would turn over just fine, but wouldn't start. I waited and tried after 15 minutes..No start just engine turning over. I had a friend come and tow me home. We pushed it into the garage and I hooked the battery charger up and let it sit. The next morning I put the key in it and it started right up ???????? Does anybody have a clue as to what is happening? I am afraid to drive it for fear it will happen again.. There has been no symptoms at all, everything runs as normal