Symptom fluctuations during Rifaximin

On day 6 of Rifaximin for IBS-D/suspected SIBO after a bout of food poisoning a few months ago. Took Rifaximin 5 years ago and it cleared up a similar months long bout of IBS-D pretty fast with minimal sides. I’m also taking Florastor between doses.

This time, first dose made me feel flu-like and anxious. After that passed, I felt like I had flu aches and malaise through day 2. Cleared up day 3 and my movements suddenly started to improve and get more formed. By day 4 felt really good, but then last two days the loose stools are back. Is this fluctuation normal during a course?