I’m not a medical professional, but my understanding is that an “epidural” is an injection of an anaesthetic drug (by catheter) into the epidural space. That is

I’m not a medical professional, but my understanding is that an “epidural” is an injection of an anaesthetic drug (by catheter) into the epidural space. That is, the spinal canal, where the spinal cord and spinal fluid reside. The drug has a higher specific gravity than the cerebrospinal fluid, so it descends in the canal and anesthetizes the nerves along the way. If you had an epidural while upside down, it could eventually reach your brain.