Will I be sedated for a rigid sigmoidoscopy? What is a rigid sigmoidoscopy?

Usually no sedation. Rigid sigmoidoscopy is a short, straight scope that is used to examine only the rectum and lower part of the sigmoid colon. This exam usually only takes a couple of minutes and is typically done in the office without sedation.
Sedation is common. Most GI docs provide sedation for any invasive procedure like sigmoidoscopy. The difference between a flexible and rigid sigmoidoscopy is the scope used. The rigid sigmoidoscope is less not flexible and is usually more painful than the flex scope. It does give the endoscopist better view so that is probably why he is using this option on you.