What is the reason of headache and neck stiffness every evening?

Stress likely: Your neck is the crux of stress and constant movement. Most everything anyone does at any job necessitates bending your head down to look, type, study or use your hands. Neck stiffness and headache occuring at the end of a day generally points to overuse or stress motion. Try to unwind at the end of your day doing gentle neck and shoulder muscle releases and rehydrate & you may see improvement.