If this guy was on his forth mid of the week, he had three days where he had all day to get some sleep.
It isn't normal for the human brain to be sleeping during daylight hours. Doing so takes a lot of adjustment and really puts the internal mechanism out of whack. If he didn't have this shift in a while and all of a sudden gets these midnight shifts, it could be very difficult for him to get sleep in during the day. It can take a week or longer for that adjustment (sleeping during day and working at night) to occur.
Controllers deal with these shift changes for their entire careers.
This fellow fell asleep very early in the shift, and within nine minutes of making the last transmission prior to 1012's attempt to reach him. While I don't disagree that the body wants to sleep at night rather than during the day, it normally manifests itself as simply not being as sharp as usual; NOT as falling sound asleep, and sleeping through multiple radio transmissions and ringing phones. And with 20 years experience, this controller must surely be familiar with how his own body deals with such shift changes, and has learned how to cope with them.
I suspect that we'll be told there's some underlying medical reason for this incident.