Not everyone has a bad reaction to Mirena, but in my opinion it just isn't a good idea to put the extra hormones in your body. If I were you I would voice my concern about the synthetic hormones and see if there is an alternative.
Most of us were told that the hormones were very minimal and wouldn't leave the uterus, but that just isn't the case. The hormones have traveled throughout our bodies and caused all kinds of weird and unexplainable symptoms.
I'm sure if you have been googling Mirena that you've come across posts of many women who have not had any problems with it, but I certainly wouldn't recommend it.