I am sure you will get many different responses to this question. There seem to be many varying degrees of severity with CAH. My son is just over 2 years old. His endo's instructions are to page her immmediately if he vomits. I have the injection and have been trained to give it and we live quite close to a great Children's Hosptial. Last spring he vomitted for the first time. He wasn't really himself for most of the afternoon, he had a few loose stool diapers, then he refused dinner (never happens!). He went over to lay on the couch and threw up several times within the space of 10 minutes. I was scared to death and paged his ped endo. She asked how my son seemed. At that time he was slouched into my shoulder, but otherwise seemed fine. We decided he should get the injection, but I had never given it before and was nervous. His dr. recommended going to the Children's Hospital (we are only about 10 minutes away) and giving the injection to him in front of a nurse who could help me if needed. Well, by the time we got to the hospital he was alert and excited and wanted to play in the emergency room kid area. We literally had to drag him back to a room. I was almost embarrassed - thinking I had overreacted. We decided to give the injection anyway, and I am glad, we did given the danger if he needed it and didn't get it. We then doubled his dose for about 36 hours. Sorry I can't remember exactly how long. While at the hospital, they tested his diaper and said he had rotovirus, but I think they were wrong because the test only took about 15 minutes and other dr.s have said that can't be. Also, he recovered way too quickly. Anyway. . . He bounced back very well. Never vomitted again and was a bundle of energy for the next week. I of course, was sleepless and exhausted. Hope that helps.