Never missed a flight after checking in, though came close once.
US west coast connecting via IAH to ORD with an overnight at IAH - stayed air side overnight. Last AA flight in, one of the first out.
Found a nice place to sleep as suggested by sleepinginairports.net. Set my alarm.
A few hours later, wake up to find alarm didn't go off (seems my phone's alarm won't activate when headphones are plugged in) and aircraft door closing in 5 minutes. In my rush to get everything packed up, shoved into bags and rush to the flight, I didn't notice my noise cancelling headphones fall out of my bag until after pushback. Had to buy a new pair in ORD before my next long haul a few days later.