“excessively righteous.” In this context, “righteous” is being used as doing right and righteous actions. Some people are overly worried about making a mistake or not doing enough for God and others. While it is good to want to do what is right, we will never be perfect, and that concern adds pressures to life that can affect one’s mental and physical health, just like the verse says.
Another aspect of being excessively righteous is that there are times when strictly enforcing a rule is clearly wrong (for example, a person rushing to the hospital with a dying person in the car, and running a red light when there are clearly no cars coming does not need to get a ticket for running a red light). Thus, the New Testament tells leaders to be “reasonable” (1 Tim. 3:3).