Manuel has recently learned that his favorite grandfather is sick and is going to die within the next six months. although he is only 7 years of age, manuel has started displaying some curious symptoms. he has frequent headaches and stomach pains with no physical explanation, he has become unusually moody and irritable, and he has lost interest in his favorite toys, video games, and television programs. given what is known about the expression of mental illness in the young, what is the likely cause of manuel's symptoms?