When it's the middle of the day, and you realize you have a lot to do and not enough time to do it. As a result, your mind locks up and you can't work, you just sit and pity yourself.
Usually caused by procrastination.
When you procrastinate too much and end up having multiple huge assignments (which you haven't started) due the next day, you may have a mid-day crisis, and end up laying on your bed throwing a tennis ball at the wall. Eventually you either say "fuck it" and don't do the assignments, or you get off your ass and work on them all night.