Feeling pain with nerve damage

[AmericanChai]

I was just wondering about something and seeing if anyone has observed or experienced this with any patients.

If a person has no sensation in a body area, can the body still "feel" the pain and react in the same way as a client who does feel pain? For example I know a boy who gets frequent bladder infections. He had a birth defect that causes him to not feel sensations in his bowel and bladder but otherwise he can still walk and feel sensations everywhere else. In a normal person, a serious bladder infection might cause the person to have higher BP and heart beat because of their physical and emotional distress to the severe pain, in addition to the normal symptoms of fever, problems voiding because of swelling, etc. This boy has no sensation and doesn't know he has the infections until the cultures come back (he gets a lot of cultures to keep an eye on his condition). His mom swears that he can still "feel" the pain even though he's not aware of it on a conscious level. Another example would be a person who has a spinal cord injury and cannot move or feel their legs, but they get a severe infection or injury to one of their limbs. Or what about a person who's in a long-term coma and gets an infection? Would you treat them for pain or not?

So if they can't feel that pain, would they also have high BP or other things that clients get when they are in great pain? Does their body still feel the pain even if their brain doesn't interpret the pain in a conscious way? If you gave such a client some pain meds, would there be a difference in their vital signs, etc. in a measurable way? Would the pain meds make them feel better and speed their recovery, or would not not make a difference?

BTW I'm a nursing student so I have no clinical experience with this.