med student here. not a doc yet, so don't take this as gospel:

Your nerves don't work intuitively once you get inside your gastrointestinal tract--pain is generally interpreted as pressure. The line between dull and sharp pain in your GI system is called the pectinate line, and it's only a short distance up. When your ass hurts like hell after a shit, that's often because there's a tear on the outside. When you see bright blood in your feces but it didn't seem to hurt, the injury was deeper. Injuries that are above the pectinate are the more dangerous of the two because patients don't feel pain, and as a result, don't feel the need to get it checked out.

The other important thing to consider about this area of injury is that two different venous systems (portal and systemic) come together in that area. In other words, any bad bugs that get in there can take a highway to your liver. A minor infection can probably managed easily, just make sure you visit your doc (they see 'adventurous' people all the time, so don't let potential embarrassment keep you from going) so they can make sure you're OK and give you better and more accurate advice than a random first-year med student on the internet.

TL;DR- injury to your guts can be significant, but painless. Go see your doc.