Hello, I m sorry that you have to go through a tough situation in your life as a family and I do understand your concerns. As I understand from your statement, your husband has been having episodes of vomiting and possible dehydration. It would have been much helpful if there were few additional details described below were mentioned. 1) Age 2) Frequency and color of vomiting 3) Presence or absence of fever 4) Ability to tolerate liquids or solids (Swallowing) However, with the limited information available I can answer you how to convince him to visit the ER. As your husband is already a chronically ill patient, he will not be able to tolerate severe dehydration. If he is not able to hydrate (take liquids) adequately he will loose electrolytes from his system as there are no other way by the body to replenish them. Once there is electrolyte disturbance, there is subsequent reactions like increased heart rate, abnormal heart rhythms, palpitations, sweating that can progress to severe shock. The tiredness that he is experiencing is due to loss of electrolytes and lack of energy as he had not eaten anything significant lately. If he finds it difficult to eat or drink then it is advisable to visit the ER at the earliest as the lost electrolytes and fluids can be replaced intravenously. Moreover, it is even possible to establish the root cause for the vomiting. It can possibly be due to several factors starting from his cancer medications to common infection. Hope you have enough information to convince your husband now. Regards, Dr Manoj Pradeep MD