Next time you go plan a vacation, you can extend it for more than a week (for those who find it hard to ask for leaves), because thanks to some really cool, intelligent people, we have research-backed proof that an ideal vacation should be 8-days long. 

vacation
Source: INC

That's correct. Apparently, you need 8 days for happiness to peak when you are away from work. I personally think I'd need around 80 days for that but that could just be me.

8 days is also the amount of time that people need on average to get accustomed to a new place and get over emotional hurdles (again, this is subject to a lot of other factors).

Ideal Vacation Duration
Source: Book It Forget It

What's most interesting is that after the mentioned amount of time, the sense of excitement starts going down, and hence, it may be the right point to go back home.

Journal of Happiness Studies published a full-blown paper on this topic and have reached a conclusion that anything less than a week is not ideal for your mental wellbeing but it will still help so don't miss out on those.

Here's a graph of a person's health and wellness over the course of 6-8 days of vacation, as published by the journal.

ideal vacation days
Source: Journal of Happiness Studies

You can show this graph to HR next time. Hopefully, it will all work out for you. You're welcome.