Acupuncture needles are very thin, smooth and flexible—about the thickness of a human hair. They have no resemblance to an injection with a hypodermic needle, since the main source of pain from injections is from the large bore hollow needle and the medication being forced into the tissues by pressure.
 
Ordinarily, upon insertion of an acupuncture needle, people will experience varying sensations. This ranges from no pain at all, to a slight pinch, a feeling of heaviness, warmth and achiness or possibly tingling and an electric sensation during a treatment. The needles are retained for 20-45 minutes and people often become deeply relaxed and sometimes even fall asleep. After needle removal, you may feel energized, sleepy or lighter. You may notice immediate improvement of your symptoms.