In this case, the unconditioned stimulus is; Chemotherapy.
Cancer are group of diseases caused by rapid growth of abnormal cells in the body. Chemotherapy is a treatment that involves the use of medications (anti-cancer drugs) to treat cancer. Chemotherapy causes various side-effects (as a result of the damage of normal cells of the body that rapidly increase). Nausea with vomiting, are common side effects that is usually experienced by cancer patients that are receiving chemotherapy.
