I take Lexapro + Abilify at the same time everyday. No serotonin syndrome.

SS is very rare just like Lamictal SJS rash is very rare: Prevention, Recognition, and Management of Serotonin Syndrome - American Family Physician

Edit:
there are roughly 325,000,000 people in the US and 46,000 SS cases. That's a 0.014% chance of getting it. I wouldn't worry about it