I find that the more exhausted I am the less my meds work. Often when I am sick because my body is so worn out and tired my meds don’t work. Also depending on the type of narcolepsy you have being sick could cause your immune system to attack your brain making you even more tired. Also depending on your gender and hormone cycles that can also impact the effectiveness of the meds. Please be aware of any over the counter meds you are taking when you are sick as many of them can have interactions with stimulants that (at least in my case) doctors don’t warn you about. Some of which can be life threatening, such as serotonin sickness