What Causes Vomiting And Constipation While On Xalkori?

My mother in law has advanced stage lung cancer NSCLC. She was diagnosed over a year and a half ago and was all ready at stage IV at the time. She has done well overall considering. She has been on Xalkori and has had to have radiation to some select areas of her body due to increased cancer activity and associated pain. She is definitely changing and I would say declining. Needs a lot more sleep. Limited stamina. Over the past week or so she has had spells of vomiting while she is trying to have a bowel movement. She has severe constipation from having to take so many pain meds. She is on oral morphine twice daily and has to take additional pain meds like Oxy at times. I am just wandering what is going on in her body with the vomiting while she has having a bowel movement?