Chi or Qi energy flows in the body thru pathways, other known as meridians. It is the base of the Traditional Chinese Medicine.
That is why it’s believed that with acupuncture the blockage of the Chi energy is released. In that manner the energy flows better thru the body and the function of the body organs is improved. Otherwise that blockage will lead to illness.
Each meridian contains pressure points. With stimulation of them by acupuncture, or acupressure, the Qi energy is released and the tension in the body is reduced.
Similarly to this, it is believed that by putting an ice on the neck (on a specific spot) you can improve you mood, overall health, while feeling energized at the same time.
This specific spot on the neck is known as Feng Fu Point.
In Traditional Chinese medicine it is believed that ice can energize the body and provide physiological balance.