Why is my internet down every night?

For some reason, my internet goes out between 1-2 am. Currently it's 139am and both my routers are down. This is terrible for 3rd shift on call medical who rely on the internet to look at patient charts and save lives. Why does xfinity always have to interrupt service for updates? Verizon never had this issue. For as much as I pay I should never have interrupted service, let alone almost every night.