I tried vegetarian for a week or two when I was in high school, then I quit because I just felt like crap, and I really wanted a juicy, fatty, salty, steak.
A couple years after high school, I went on a Mexican/Central American/Carribean kick, mostly because I fell in love with chili peppers, and also rum and tequila played a part as well. I also dabbled in Asian and Mediterranean style cooking, although what I ended up doing was far from authentic. I was still eating bread and corn/rice and beans, but I was doing things right mostly, as I did away with most processed foodstuffs.
I came upon paleo about two years ago, and didn't give it much of a nevermind until maybe a half year after then. I didn't really see myself as in bad health (I was 22 years old, 6 feet tall, and about 195 lbs.), but after cutting sugar, booze, and excessive starches, I went down to about 160 lbs, and finally did see how bad off I was.
So I never really had a "wake up call", but rather a gradual evolution into a more healthy lifestyle.
"All of God's creatures have a natural habitat... my dinner plate." -Me