How long does it take for side effects of xeomin such as aching muscles, head ache, sore throat, and fatigue, to resolve?

Since you've had Xeomin before, it is unlikely this is the cause. If it persists, I recommend getting a formal evaluation with your Doctor. Best, Dr. Emer

The flu like syndrome reported with cosmetic botulinum toxin treatment like botox, dysport, or xeomin is actually a form of mild botulism.  Some individuals are just more sensitive to the systemic effects of these treatments.  It is rare but well described.  When the symptoms are short lived (days) and the cosmetic effect profound, people put up with these side effects.  When symptoms persist then it is hard to ignore them.  Seeing your doctor and determining if you symptoms are from a cold or the result of sensitivity to the botulinum toxin is appropriate.  The persistence and unpleasantness of your symptoms should guide your choice to have this type of service in the future.

Your dose of Xeomin was a very low one.  Since it was so low and since you've had it before without problems, I seriously doubt that the symptoms you are describing are due to Xeomin.  I think it much more likely that you have some sort of viral illness.  If it does not get better in several days, I recommend following up with your primary care physician.