Sounds like a UTI (upper respiratory infection). If so, it needs to be treated with antibiotics. If one is prescribed, please inquire about getting a probiotic as well. Every antibiotic needs a probiotic so it does not upset rabbit tummies.
For URI treatment, the sooner, the better. It’s a bacteria, so the longer it has, the more it multiples and the more you need to treat. It’s not an emergency where your rabbit will stop eating or using the restroom (if that becomes the case, yes an emergency vet), but again, the sooner the better.
When Wick had a UTI, I set aside a sack of soft clean hand towels just for him. If I saw he had an especially bad sneeze attack, or just happen to see he’s a bit of a mess, I would damp a towel, gently wipe his nostril area, then use a fresh towel to dry it gently. Being there to pet your rabbit following a sneeze attack is not a bad idea. Wick liked it.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.