Today I flew from Hawaii to Japan. Or was that yesterday? Actually, I think it was both days!
I set off from Honolulu at 11.45 am on the Monday 26th Jan, and after a nine hour flight arrived in Tokyo at 4.00pm on Tuesday 27th Jan, over a day later. This is the first time I have ever crossed the International Date Line, and have lost a whole day!
Hopefully I will get it back sometime in the future, perhaps if I travel the other way around on the next trip!
More on the International Date Line:
Wikipedia
WorldAtlas.com