Anyone here taking Flexeril while on Zoloft?

Yes, there is a major interaction between both meds as you point out.

Now, if the same Dr. prescribed both the antidepressant and the muscle relaxant, he/she is most likely to be aware of the potential interaction and would not put you in harms way, but if two different Drs. prescribed each medication without knowing you were on one or the other I would not take them until you inform both of the prescribers, or if you are self medicating, by that I mean the cyclobenzaprine (Flexeril), again, I would inform your Dr. that you are planning on taking the muscle relaxant once in a while, but never self medicate.