If you think you might need a holiday check out the stress test.

I am not sure exactly how it works, but this is amazingly accurate.
Read the full description before looking at the attached picture.

The picture below has 2 identical dolphins in it. It was used in a
case study on stress levels at St. Mary's Hospital. Look at both
dolphins jumping out of the water. The dolphins are identical. A
closely monitored, scientific study revealed that, in spite of the
fact that the dolphins are identical, a person under stress would
find differences in the two dolphins . The more differences a
person finds between the dolphins, the more stress that person is
experiencing. Look at the photograph and if you find more than one
or two differences you may want to take a vacation.

Incidentally this is the study that I would use to justify my need
for holidays!.