Mall hangover refers to the headache, tiredness and sometimes nausea one gets after going to the mall, just like many may experience after heavy consumption of alcohol. A hangover describes the sum of unpleasant physiological effects following heavy consumption of alcoholic beverages, typically after the intoxicating effects of the alcohol begin to wear off. This is exactly where the term comes from.

“商场宿醉反应”（mall hangover）指逛完商场后出现的头痛、疲劳及偶感恶心的症状，就跟人喝醉酒以后经历的不舒服的感觉一样。Hangover这个词本来就是指喝醉酒以后、尤其是酒劲散去之后出现的不适反应。Mall hangover便是由此而来。

For example:

I was at the mall for like five hours and when I got home I had a major mall hangover.

我在商场待了大概5个小时，回家后就出现了严重的商场宿醉反应。