According to Wikipedia,
Post vacation blues (or just vacation blues) or less commonly, post travel depression (PTD) is a type of mood that persons returning home from a long trip (usually a vacation) may experience.
Background
A person may suffer from post vacation blues after returning home or
to a normal routine from a long vacation, especially if it was a
pleasurable one. The longer a trip lasts, the more intense the post
vacation blues may be. This is because the person would be longing for
their travel experiences. Post vacation blues may result in tiredness,
loss of appetite, strong feelings of nostalgia, and in some cases, depression. Jet lag may intensify the post vacation blues.
Treatment
In general, post vacation blues wear off after time. It usually
takes a few days for the mood to wear off, although in some cases, it
can take up to 1.5 times the length of the trip. Other ways of treating
post vacation blues are for the person to share their experiences with
family and friends, or to look at photo and souvenirs.
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Tiff Gag 說
1.5 times the length of the trip
tht's 7.5 yrs for u
(ono~~)