My guess is that you don't have a fixed IP address and the ip address changed. Changes to dynamic addresses often happen overnight.
If I am right then you will need to either get a fixed IP address or set up a dynamic DNS domain name. The former is between you and your ISP. The latter depends on whether your router supports dynamic DNS, and if so which one(s). It probably supports dyndns. There are many posts in the calibre forums about using dyndns. See http://dyn.com/dns/dyndns-pro-free-trial/
. You can get one hostname for free.
If you have a static IP address from your ISP then you might have a dynamic address for your mac. If so, then port forwarding will break when the internal IP address changes. The solution: give it a fixed IP address, probably best done using a static DHCP lease in the router.
Isn't networking fun?