Does Taking Cymbalta And Prozac Together Cause Serious Drug Interactions?

I asked my doctor if I could add anything to my daily 60mg Cymbalta (duloxetine HCL DR) prescription to help with increased depression over the last 5 years. He thought that we could try replacing the Cymbalta w/Prozac (fluoxetine HCL 20mg), which has worked well for my mom. I have severe w/d symptoms as quickly as 36 hours between doses and am prepared to face th, then at, however he has me going off Cymbalta 60mg every 36 hrs, then 30 mg, then 30 every 48 hrs, and go from there while starting Prozac 20 mg/daily. Are there serious interactions I should be aware of? What should I look for? When should send me to the ER? I have experienced Serotonin Syndrome before. Is that a side effect? Should I not combine these drugs at all or is taking both permanently an option if I don t have any side effects?