I am a 2nd year ob/gyn resident. First let me just correct the statement in the previous post. Most ob/gyns do NOT drop obstetrics as soon as they can. That is simply untrue. No one is forced to do obstetrics. There are several jobs available for gynecologists only. Ob/gyns stop delivering babies due to malpractice rates, family issues, and those nearing retirement who are trying to phase it out of their practice.
Now on to the stamina question. We get tired just like anyone else. It depends on the type of residency program you attend. Some residents actually get to sleep on call. I am a resident at Parkland, so often times you are busy the entire time you are there. Most of the time, you don't realize how tired you are until your shift is over. There are always exciteng things going on. Once you become a resident, your whole perspective is different. You know this mom is depending on you to take care of her and her soon-to-be infant. With this specialty, things can take a turn for the worse in a heartbeat! How awful would you feel if something drastic happened and you couldn't perform because you were just too tired? This is where the adrenaline rush comes in. If you are passionate about what you do, things like stamina tend to take care of themselves.