Acute SIBO is a thing, but I think it much less common than chronic SIBO. So you have to consider all possible causes of your symptoms. I can't make personal recommendations for NAC, though general guidelines are usually provided by manufacturers. Ideally, you should consult a professional experienced in dealing with gut issues, and get tested. The Fodmap diet works for all sorts of GI problems. Although fibre is considered to be important, for many people it can make their symptoms worse.