If I'm the named executor of my mother's Will but due to health reasons it is impossible for me to serve, can I refuse?

Yes you can decline to act as the executor of your mother's will; I hope your mother has an alternate named to be the executor; if not then someone else in the family could petition to act as an executor; if no one is available, then a petition in probate court , for the appointment a financial fiduciary could act as the executor.