Some are younger, others are older when this happens. This is another area where medical science does not have answers yet. There also appears to be a cumulative component to HNPP symptoms and activity. We tend to think of each nerve as one nerve. In fact, there are many nerve fibers making up the one nerve.
Some people report being able to do an activity one day without any problems.
But have increasing symptoms if they continue to do the same activity many days in a row. When people experience increasing problem such as this, they are thought to be damaging more and more of the nerve fibers. Although nerve fibers are probably damaged on the first day of the activity, there are enough fibers still functioning to compensate for the damaged ones. As the activity continues, more and more fibers are damaged and the symptoms become more apparent as the nerves are unable to continue to compensate for the injury . Recovery from palsy episodes is usually complete at first with numbness and weakness going away entirely.