Why is it that if one was physically injured or endured pain somewhere on their body, that they can "feel pain" at a later date when just thinking about the incident?

Nerve memory.

What marinelife said. Your nerves do strange things. Amputees get phantom pain in their missing limbs. Figure that out.

An extreme of this is phantom pain, feeling the pain of a leg that has been amputated is an example of this. Literally there is no foot there to be felt, but the person perceives pain in their foot. The brain still has all its parts so it can imagine or feel the foot. It has the memory of the foot. This can be true for anything probably. The nerves are misfiring, the brain is tricked somehow.

It’s a combination of all 3 things mentioned plus if its still injured, like if you had a broken leg and it hasn’t quite healed yet, it’s your brain telling you that you’re still injured and need to be careful so you don’t make it worse.

Wow… It must have hurt really bad if you can still feel it afterward.

Memory’s a powerful thing; even if you don’t consciously remember something, it’s there. I think we remember the pain, then our brain recreates the pain from that memory.

I don’t think it only applies to physical injuries. I still feel generalized physical pain and nausea when I remember too many details of an emotionally painful experience.