2001 Alero won't start

I parked my 2001 Alero GLS and upon return 15 minutes later, the car would not start. Would not crank, or turnover...just nothing. No click, no whining, nothing. It was just like the battery was disconnected BUT I've got full power in the battery, that's not it. After turning the key over and over (about two dozen time) It fired up like nothing was wrong. I'm looking for any help I can get to figure this out. Talked to a mechanic and he said "...haven't heard of an Alreo doing THAT. I don't know what it would be" Help.

sounds like maybe a bad spot on the starter... possibly bumping the key moved it enough to make contact again.