During a vaginal birth after cesarean (VBAC) trial of labor, you can be given a sedative in the form of an injection into a vein. A sedative does not block pain but does help you relax and sleep during the early part of labor, allowing you to conserve energy for active labor and delivery.
Depending on when you take it, a sedative can make it hard for you to remember the details of the birth.
WebMD Medical Reference from Healthwise