I feel really bad for not going out?

I'm literally exhausted as I'm writing those words. I will be going to Thailand in two days for a period of six months and I still have a few things to do before I got, not to mention that I haven't researched anything on the country.

I've been working like crazy for the passed 4 days and I just want to sleep tonight before I get up and finish everything but two of my friends really expected me to go out and they had been pressurizing me all day. They said I should go out because it's my friend's birthday and it's also my last night but that's precisely the reason I don't want to go. I'm so tired, I'm feeling ill and I just want to feel rested before I go. Is that not normal?