It happens to the best of naturals; HECK, it happened to me! HEAT DAMAGE!
It's one of the reasons lots of Natural Haired ladies don't experience the growth they'd like to see. And it's one of the most difficult mistakes to fix when it's noticed.
Essence.com published a great article on recovering your hair after using too much heat.
The point of the matter is, once damage is completed, you have to be diligent about your routine to regain your curl pattern. Sometimes it's just changing your shampoo/conditioner routine, your diet, or you may even have to get a hair cut!
But it's all a step on the journey of healthy natural hair.