Why do mantras help me sleep better at night during stressful days?

Hi, I am Riya Singh. Mumbai is the place I call home. It was there I came into the world on the 21st of August 2000 at 11:30 PM. As a rule, if I had a stressful day, I would not have a good night sleep. My brain keeps running through various thoughts especially unfinished work. A friend of mine just recently suggested that I chant "Om Shanti Om" before I go to bed. I only did it once last night, and my sleep was very quick and I felt more relaxed. Surely, I am amazed to find out chanting mantras as a sleep aid and also how I can use them during the day to fight with my anxiety.