I Am Currently Taking 20 Mg. Of Lexapro And My

I am currently taking 20 mg. of Lexapro and my doctor recommended Zoloft instead of the Lexapro. Both are SSRI drugs, why should I change if both drugs do the same thing? I have PTS from a car accident that killed my partner 6 years ago. I don't perseverate on the accident but I still can get easily upset when I think about it. In addition I have a damaged aorta from the accident as well as having been on Kepra for possible seizures, (I also received TBI from the accident). The side effects from switching medications scares me. Any advice?
Thank you-Tracey Mammarellitmammarelli