I'm not sure if stress effects the hair, but your hair can change with time.

How do you style your hair when you want it curly? I went from having a natural wrinkle more than curls and it was super fuzzy. I discovered two keys that have made my curls come through. The first is I quit brushing it. I finger comb in when my hair is wet as I put the conditioner in. I no longer wrap it in a towel, I scrunch it gently in an old T-shirt. The second is finding the right product. For me, depending on how long it is, I use Divacurl Angel and/or Aveda's be curly to encourage the curl and allow it be be soft and bouncy. If you Google "curly girl" there are more detailed instructions.