Happy Thanksgiving! Next week, President Obama will issue a pardon to another fortunate turkey while most of us partake in the yearly ritual of gorging ourselves on succulent turkey meat. Afterwards, a satisfied, sleepy feeling will hit us like a ton of sheep. Some believe that turkey dinner makes people sleepy because it contains tryptophan, an essential amino acid. In fact, some people actually take a supplement containing L-tryptophan to treat insomnia, anxiety and depression. What is the...