What are the symptoms of withdrawal from motrin/tylenol if there is withdrawal from these meds?

A friend of mine is experiencing lethargy and general malaise following sudden cessation of 2400 mgs daily of motrin, supplemented with 1000 mgs of tylenol for back pain as prescribed by his doctor for over a year now. Within a few days of altering his normal intake, he began having what appeared to be flu like symptoms with a general lack of energy. Is this attributable to the cessation of those two medications or is it unrelated?