This happens a lot when I'm sitting in class, and it gets kind of boring. I try to stay awake, then suddenly everything goes hazy and I black out for a second. Sometimes I'll even have strange half-dreams right before it, like hearing voices that aren't actually there.
DESCRIPTION
The usleep() function suspends execution of the calling thread until
either useconds microseconds have elapsed or a signal is delivered to the
thread whose action is to invoke a signal-catching function or to termi-
nate the thread or process. The actual time slept may be longer, due to
system latencies and possible limitations in the timer resolution of the
hardware.
This function is implemented, using nanosleep(2), by pausing for useconds
microseconds or until a signal occurs. Consequently, in this implementa-
tion, sleeping has no effect on the state of process timers and there is
no special handling for SIGALRM.