Sudden Kinky Hair
A: The only way to explain such an occurrence would be that you have exposed the top layer to something which has caused a change in the hair's texture.
You should carefully review everything you've done and exposed your hair to in the time prior to the hair becoming kinky. You should also examine your hair for signs of damage - dryness, roughness, straw-like feel. If you notice any signs of damage, you need to be sure to condition the hair thoroughly to prevent further damage.
Hair doesn't spontaneously change its texture or wave pattern overnight. There is usually some environmental or other factor that causes the change. Without knowing what you may have done, where you may have gone, and what you may have been exposed to, I have no way to even hazard a guess as to what may have caused the sudden change in your hair.
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See also:
How to protect your hair while you sleep
Heat styling basics
Weather and your hair
Analyzing your hair