What would cause early evening nausea that is just felt in head and subsides within an houror so?

Nausea: If the transient nausea only occurs in the evenings it may be related to the supper meal. Eating certain carbohydrates,especially sweets, may cause fluctuations in blood sugar from high to too low an hour or so after the meal. If there e is associated dizziness from inner ear disturbance, nausea may also occur. Take note of what you eat and whether there is dizziness with the nausea. Nonpregnant?

Sinuses: Sounds allergic or sinus related. Your head is filled with sinuses. Sometimes these can get congested; perhaps you perceive this as "nausea". Maybe, by the end of the day, allergens get the best of you. Try a warm shower followed by some hot tea just before you get this and see if it helps.