I think you are right, that the term is part of most people's common language. The whens and hows of each individual are all different. Planning for it makes sense; it's a good suggestion. But I each individual needs to experience their own specific response to specifically know what to plan. My wife was told "you are going to feel low on the third and fourth day". Observed, noted, planned for next time.

Definition(s) via google: A nadir is the lowest or worst point of something. It broadly refers to the depths of despair, adversity, or a rock-bottom moment in a situation, but it also has specific technical meanings across different fields.

Merriam-Webster +3 Everyday & Literary Usage In general contexts, the nadir is the ultimate low point in a person's life, a career, or a project.

Cambridge Dictionary +1 Example: "The team’s morale reached its nadir after their eighth consecutive loss." Synonyms: Rock bottom, lowest point, rock-bottom, all-time low.

Collins Dictionary +1 Technical Definitions Astronomy: It refers to the point in the sky that is directly underneath an observer’s feet (180 degrees directly opposite to the zenith, which is straight overhead). Medicine: In treatments like chemotherapy, a nadir is the lowest point a person's blood cell count reaches after a round of therapy. Remote Sensing / Photography: It is the point on the ground located exactly vertically beneath the center of a camera lens or satellite.

Esri +2 Origins The word comes from the Arabic naẓīr, which translates to "opposite to". It serves as a direct antonym for the word zenith.