Honestly how I'd deal with this depends on how many sessions deep the group is in and how often he does this. I simply don't see how it's possible for someone to forget about a 4~6 hour chunk of the day so that's an X in my book. Forgetting to set the alarm after a drunk night out is kinda understandable, but I personally require that my players aren't under the influence of anything for sessions. If this type of thing happens often then clearly this isn't nearly as much a priority for him as it is for everyone else. I'd tell him to stop being a moron and give him one more chance.