Allergy symptoms can be worse in the morning for a few reasons.
One possible explanation is that the body's natural cortisol levels are highest in the morning, and cortisol can suppress the immune system, making a person more susceptible to an allergic reaction.
Additionally, the accumulation of dust mites and their allergens can be more concentrated in bedrooms, which people spend around 8 hour in, leading to more exposure. When we sleep, we tend to toss and turn and create more movement in our beds, agitating dust mites and releasing allergens into the air.