They just fall off???

Ok so I'm riding home on my bike the other night about midnight clippin along about 15-20 mph or so and pretty uneventful. I start going up a hill and the handlebars literally completely fly off the bike! I go flying over the front of the bike, crushing the headlight and a few of my knuckles, and hit the ground while the bike hits the ditch. Now seeing that about th weeks before I was riding along and the back wheel came compeltely off, I'm beginning to see a need to go through and tighten every bolt. I suppose I never thought about the chance of the handlebars flying off the bike while riding. I mean seriously, has that every actually happened to anyone?? what a night.