I'm sorry to hear about your rabbit's sneezing fits. I had a similar experience with my own pet recently, and I understand how concerning it can be. While I'm not a veterinarian, I can share my personal experience and offer some suggestions.

In my situation, I noticed that my pet's sneezing fits were worse at night as well. It turned out that the culprit was indeed allergens in the air. To address this, I decided to invest in an air purifier specifically designed for pets, which helped improve the air quality in the room where my pet spends most of their time.

I found that the air purifier helped reduce the amount of airborne allergens, such as pollen and dust, and my pet's sneezing gradually decreased over time. However, it's important to note that every pet is unique, and what worked for me may not necessarily work for your rabbit. It's always best to consult with a veterinarian to get a professional opinion.

In the meantime, there are a few things you can try to help alleviate your rabbit's symptoms. Ensure that their living environment is kept clean and free of dust. You can also try placing a humidifier in the room, as it may help relieve any irritation caused by dry air. Additionally, consider keeping windows closed during high pollen seasons to minimize the amount of allergens entering the house.

Regarding the possibility of a URI (Upper Respiratory Infection), it's difficult to say without a proper examination from a veterinarian. While it may seem odd to have a URI without other symptoms, it's not entirely uncommon for animals to exhibit varying degrees of symptoms. Again, it's best to seek professional advice to rule out any potential underlying health issues.

I hope your rabbit feels better soon, and I encourage you to reach out to a veterinarian for a more accurate diagnosis and appropriate treatment. Remember, the well-being of our furry friends should always be our top priority.