Everything in nature is energy and vibrates to a frequency, even if you cannot sense it. Even the cells of your body vibrate with energy, when your cells are out of harmony, the vibration of something near your body will influence your cells, causing them to vibrate at that frequency, this is called Entrainment.
When not feeling well, the frequency of vibratory instruments such as, gong, crystal or bronze singing bowls, chimes, drums, tuning forks, and others will help get the cells of your body back into harmony and allow the innate healing mechanism of the body to step in.