How can one know if the body has affects of magic or not?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

It is possible to recognize if one is bewitched or not from some symptoms and indications that give the impression of being so. Among these indications are: (1) aversion to family, home and society (e.g. tends to be alone), (2) psychological or nervous diseases such as epilepsy, (3) disorder and confusion of one's sayings, doings and thinking, and (4) paleness of face, being upset, moaning and absent-mindedness.
In general, all indications and symptoms that show an abnormal response to medical treatment might also be signs of magic.
Allah knows best.