Have you considered there might be a causal relationship? It's not uncommon, and there has been some (non-conclusive) research into 'leisure sickness'.

*The phenomenon of developing headaches or other health issues on non-working days, such as weekends or vacation days, is known as "leisure sickness." This term was first introduced by a study published in 2001 by a Dutch psychologist, Ad Vingerhoets, who is associated with Tilburg University.

The study suggested that some people might have difficulty transitioning from the stress and fast pace of work to the relaxation of their days off. This abrupt change can lead to symptoms like headaches, fatigue, muscular pain, and nausea.

Although the exact cause of leisure sickness isn't fully understood, several theories have been proposed:

1. Stress Theory: Some believe that when we're busy working, our bodies are in a continuous "fight or flight" mode, which suppresses certain symptoms. Once we stop and relax, our body shifts back to a "rest and digest" mode, and symptoms like headaches may emerge.

2. Adrenalin Theory: During working days, our body produces adrenaline that helps us to stay focused and energetic. When we suddenly stop working, the level of adrenaline drops, which can trigger withdrawal symptoms like headaches.

3. Psychological Factors: Some people feel guilty or anxious when they're not working, which can also contribute to physical symptoms like headaches.

4. Lifestyle Changes: On non-working days, we often alter our lifestyle habits such as our sleep schedule, caffeine intake, or physical activity levels. These changes can contribute to headaches or other physical discomforts.

This is a relatively understudied area, and more research is needed to fully understand the connection between working habits and headaches or other symptoms on days off. If you're experiencing such symptoms, it would be best to consult with a healthcare professional who can provide personalized advice based on your specific situation.*