As opposed to actually taking a holiday, simply planning a vacation or break from work can improve our happiness. A study published in the journal Applied Research in Quality of Lifeshowed that the highest spike in happiness came during the planning stage of a vacation as people enjoy the sense of anticipation:

In the study, the effect of vacation anticipation boosted happiness for eight weeks. After the vacation, happiness quickly dropped back to baseline levels for most people.

Shawn Achor has some info for us on this point, as well:

One study found that people who just thought about watching their favorite movie actually raised their endorphin levels by 27 percent.

If you can't take the time for a vacation right now, or even a night out with friends, put something on the calendar--even if it's a month or a year down the road. Then, whenever you need a boost of happiness, remind yourself about it.