A Few Times A Year My Mom Has Woken Up

A few times a year my Mom has woken up at 3:00 am with the feeling of having to go to the bathroom (#2). Sometime she makes it to the bathroom, sometimes she doesn't. But she always passes out in the process. She has been tested, heart and everything is fine. I'm wondering if she has a damaged vagus nerve, where her blood pressure drops in the early morning hours.