Decaffeinated coffee is not 100% caffeine free. When coffee is being decaffeinated, 2% of the caffeine still remains in it.
Chocolate is lower in caffeine than tea, coffee and coca cola. A one ounce bar of chocolate contains about 6mg of caffeine, whereas a five ounce cup of regular coffee contains over 40mg.
It has been shown that caffeine causes headaches when stopped suddenly and can cause morning headaches that are relieved by a dose of caffeine.
You can overdose on caffeine.