I haven't had a cold since getting both of my CIs, but I do have year-round allergies. When I have an allergy attack, it affects my CI hearing. Sounds become "bassy" and distorted. I also find that when I have a migraine, sounds seem louder and "sharper."
Interestingly enough, during my first CI evaluation I was put on Zyrtec for 30 days to see if it would help my hearing (due to my history of blocked Eustachian tubes and years of untreated allergies). Audiological testing revealed that my hearing "improved" from a bilateral profound loss to severe-profound in my right ear and profound in my left ear. I also discovered that I could hear vowel sounds with my left ear -- something I couldn't do for the past 10 years.
By the way, speaking of CI hearing and being sick...When I had an allergy attack the summer after getting my first CI, I informed my audi about the "bassy," distorted quality of what I was hearing and asked if I should go in for a mapping. She said no since another mapping would be required after I started to feel better. She said it was best if I kept my map as it was so that I didn't have to worry about adjusting to one map and then having to readjust to a second map several days later.
Something interesting I've noticed...Ever since my CI surgeries and being put on allergy medication (Fexofenadine/Allegra generic), I no longer have problems with popping ears or a blocked feeling in my ears.