I like to tell my patients when they ask, that Qi is what makes the difference between being alive and being dead.
Biomedicine doesn't know what makes us alive vs. dead, and they don't know what Qi is. Coincidence? I think not!
One textbook definition of Qi is "The fundamental substance of which all matter in the natural world are composed. All matters in the natural world are formed by the change and movement of Qi." (Advanced Textbook on Traditional Chinese Medicine and Pharmacology, Vol. 1. New World Press, Beijing, China, 2002.)
Another textbook similarly describes it as "The fundamental substance constituting the universe, and all phenomena are produced by the changes and movement of Qi. Qi is both the essential substances of the human body which maintain its vital activities, and the functional activities of the organs and tissues." (Chinese Acupuncture and Moxibustion. Foreign Languages Press, Beijing, China, 2003.)
Free, smooth movement of sufficient amounts of Qi is essential to health and vitality. When this is not the case, we begin to experience unhealth. Acupuncture is certainly not the only way to achieve free and plentiful Qi. Health CAN be retained and regained through healthful living, but Chinese medicine can speed the process back to health. In addition, Chinese medicine can PREVENT disease by ensuring that the amount of Qi that one has is always in adequate supply and moving properly throughout the body.
So what does Qi feel like? To me, as a practitioner, when I needle a patient and I'm aiming for the Qi, it often will feel like the tip of my needle is bouncing on the surface of a balloon. When I "get the Qi" it feels as though this balloon has let the needle in. I've heard other practitioners describe it as a gentle tugging sensation on the tip of the needle.
My patients often say that Qi feels like someone pressing on their skin at the site of the needle. Some patients will feel this same sensation of pressure run along the channel after the needle has been inserted. Some people will feel the Qi as a mild warm or cool sensation at the needle.
Perhaps it's this inability to even describe the sensation of Qi that has led so many to be skeptical of its existence? Okay, maybe it's due to the fact that there are no biomedical tests that can prove that it exists.
Regardless, Chinese medical practitioners can feel the Qi in your pulse, can see it reflected on your tongue and in your face, and can feel it through the needles. Thousands of years of patients and practitioners and positive results can't ALL be wrong.