You feel relaxed when you take a vacation, because your mind is at rest. The change in external environment makes it easier to put aside the stressful aspects of your daily life.
While we do not always have the ability to go to the mountains or travel to Switzerland whenever we feel excessive stress, we do have the ability to take a MENTAL trip to peaceful and serene locations. Sit in your chair with your eyes closed, and imagine that you are any place in the world where you can feel calm. Don't WISH you were there, but actually FEEL as if you are there. See how calm you start feeling as you mentally picture yourself in a peaceful meadow or forest. Imagine yourself being without any worries or anxieties.
Try it this evening when you get home from work. While this should not be used as an escape from dealing with problems, ten or fifteen minutes can be as relaxing as a short nap. You'll be amazed at how it can ease tension!
(see Gateway to Happiness, pp.89-90)