Post Fun Depression

[tinaman]

Why do we get sad/depressed after having a really good time / a lot of fun?

[Anna]

I don't always get depressed/sad after I had a good time, but  I still understand what you mean. 

I guess it depends on your situation in general. I only feel this way when I'm dissatisfied with my life and I try to run away from it. 

And also: a high serotonin level feels good, that's obvious and this is the primary reason why certain drugs are so addictive.