It sounds like you're talking about the scientific form of pressure points (as opposed to pseudoscience involving "chi meridians"), namely spots on the body which allow for direct stimulation of nerves and muscles to cause a great deal of pain or sometimes even muscle paralysis. As with defending any vulnerable part of your body, the key principles are a) to attempt to avoid being struck in these vulnerable areas and b) if you can't avoid or block the attack, move to reduce the amount of force exerted. I have heard people talk about building up muscle over pressure points to prevent being targeted, but most of the common points are targeted because they're at junctures where there physiologically is no muscle or other extraneous tissue to prevent targeting the nerves.
As for recovery, as with most aspects of martial arts involving continuing to fight while in pain or injured, it really comes down to conditioning. In many aspects, a pressure point strike is no different from "hitting your funny bone" in your elbow. You might immediately drop something in your hand when you strike your elbow like that, but for the most part, you "shake it out", grimace, and continue to do your usual task, compensating for the lack of fine control by relying on routine. As with most conditioning, I would caution that it's essentially a way of training yourself to work through injury, which requires injury in the first place, and training yourself to ignore pain can be a bad idea since pain is part of how our body informs us that something is wrong. Repeated or prolonged trauma to the nerves can cause permanent damage, as anyone who has suffered a prolonged pinched nerve can aver.
Lastly, some pressure point techniques don't so much focus on attacking the nerves, but the muscles, causing them to knot up. They tend to require more force and be less targeted, but this is essentially what you're doing when, say, you drive a knuckle into the thigh of a caught leg. In that case, as with any muscle cramp, keep moving and keep the blood flowing. Anecdotally, some people have success in dealing with cramps by striking the affected area, but more broadly (cupping your hand or just slapping it) to confuse the body into not focusing on a single area of trauma, but this might be more "bro science" than anything else.
TL;DR
- Avoid getting hit in vulnerable areas if you can
- If you can't avoid getting hit, try to reduce the amount of force
- If you do get hit in a pressure point, keep moving and rely on your muscle memory to carry you through movements
- If you feel it is absolutely necessary to train against pressure points, train under those conditions, having someone compress your nerve and then attempting (slowly at first!) your usual movements so that you get used to working through the pain or loss of feeling.
