I took one capsule of 5-HTP earlier today as a dietary supplement and I immediately felt really, well, good?

If you've ever taken Vicodin, it was a similar feeling of calm and happiness, but at one point I was racing around my kitchen singing songs to myself (luckily no one was home). At first, I thought the relaxation was a placebo effect because I "expected" my general malaise and depression to be repealed by the supplement, but my hypomanic episode, followed by this very "blah" feeling makes me think otherwise. I did some research and found nothing about "adverse" hallucinogenic or psychological affects that are often attributed to narcotics and other drugs ... does anyone have any information or similar experiences?