I'm not aware that there are clearly defined criteria for deeming someone to be in "remission" from any form of vasculitis. It is largely a decision for each doctor to make on a case-by-case basis.
Some doctors may consider "symptom-free" to indicate remission, others may require both "symptom-free and drug-free", and still others will want to see a normal biopsy where there was previously an abnormality (particularly in the kidney or lung). It is important to discuss this with your doctor and determine what criteria he/she is using to make the decision. A normal sed rate might be one of many factors to indicate remission, but I would not consider someone who is symptom-free and drug-free to be disease-active simply based on an elevated sed rate.
PAN certainly can go into remission, but it would be extemely rare (like never) for this to happen without medical treatment. Usually PAN requires long term treatment with corticosteroids, like Prednisone, and/or cytotoxic chemotherapy drugs, like Cytoxan. With these treatments patients can go into periods of remission. Everyone's case is different, so good communication between you and your rheumatologist is necessary. Tell your doctor everything that your are taking, including any herbal or "alternative" treatments, and follow his/her advice as carefully as possible.