Time travel crime thriller/romance involving female protagonist with epilepsy from the late 1970's to early 1980's

[DocHeat]

I am looking for a paperback book I read in high school about a woman with epilepsy who is actually a time traveler. She has a regular life but is transported back in time when she develops a seizure disorder. Somehow a female villain is able to take her place in the present and it's a race against time and death to ensure the protagonist is able to stay in the present. I cannot recall the author or any cover artwork. I'd like to revisit this story if anyone has ideas of who the author is.

 

[Matteo]

Sounds to me like Breakthrough by Ken Grimwood author of the fantastic Replay.