How would taking melatonin work during the day to calm me down?

Would not: Melatonin is produced in the brain to help maintain the body's internal clock. So when it is dark you produce more and when it is light you do not make as much, therefore it is intended for sleep. Try to find the root of your anxiety as a first step and consider looking in to the herbal passion flower that has been used for anxiety. Also research GABA that is known to affect anxiety.

Melatonin: Is a sleep aid. If you are stressed or anxious during the day consider options like cognitive behavioral therapy, acupuncture. Tai chi. Qi gong, deep breathing exercises, progressive muscle relaxation, massage therapy, acupressure, exercise & communing with mother nature.