Hello Michelle,
 
It sounds as if what you are describing about your friend is a type of physical seizure brought about by psychological stress.     The best thing you could do for your friend is to persuade him to see a Doctor.   Some seizures can be life-threatening if left untreated.
 
You could have a look at this site which will explain seizures and the reason for them -
 
http://www.epilepsynse.org.uk/pages/info/leaflets/factsnea.cfm
 
Talking about what happened in the past in his relationship with the woman would also be beneficial.   If it was very stressful it will take him some time (years) to begin to recover from its effects on him.     Some Christian "non-judgemental" counselling would therefore be an advantage - he need not fear being "possessed" by the Devil, if he loves the Lord Jesus Christ.    What he needs to do is to be released from the "strong-hold" his memories are causing in his mind and soul and spirit, and which are affecting his body.
 
Peace to you in the name of Jesus -   Here is a verse for you both -
 
2 Timothy 1:7   "For God hath not given us the spirit of fear;  but of power, and of love, and of a sound mind."
 
God Bless you both  -   Annette