After acupuncture treatment, you may feel tired or a little drowsy. If you feel sleepy, it is best to avoid driving/using machinery until the effects have worn off.
Other reactions may include mild headache, feeling faint and (rarely) allergic skin reactions. In the short term, you may notice a worsening of the condition for which you originally sought treatment. Although discouraging at first, this can be a good sign, as improvement nearly always follows.