Post-vacation blues

[...] In general, post-vacation blues will wear off over time. It usually takes a few days, but in extreme cases, the mood can last for several weeks before wearing off. Faster ways of treating post-vacation blues are for the person to share their experiences with family and friends, or to look at photos and souvenirs. Some may find comfort in re-living their holiday/vacation experiences; for example, if one really enjoyed jet-skiing during their holiday, they may purchase their very own jet-ski for personal use. Another well-known method of curing post-vacation blues is to plan or book the next vacation, this offers a distraction and also provides the person something to look forward to. [...]

https://en.wikipedia.org/wiki/Post-vacation_blues