Ah… I always have to struggle with keeping awake during lectures/tutorials; especially those that are right after the lunch breaks in the day. Finally a solution and explanation is explained by New York Times:
Q. What is happening in the body that it craves rest after lunch?
A. First, the 24-hour cycle of the body, or its circadian rhythm, is naturally in a resting phase at this time. In the afternoon, it happens to converge with another physiological cycle—known as homeostatic—that measures the amount of time spent awake and that is also pushing for a rest.
Add the effects of food, which can also induce drowsiness, and an overpowering desire to sleep may result.
What’s the best way for one to overcome the urge to nap after lunch?
Unsurprisingly, to take a short nap. Also, ditch the caffeine shot to get the awakening boost. It can affect your ability to get to sleep that evening. Instead:
Simply get up and move around the room. If you need to talk to a colleague at another desk, this could be the ideal time. It also helps to arise at the same time every morning, Dr. Dinges said. He has found that getting up earlier than usual—even as little as a half-hour earlier—magnifies drowsiness in the afternoon.
Now if only they provide a solution to not sleeping during my morning lectures/tutorials…