When you wake up and are hit with the remembrance of last night's out of control shopping escapade.
There are a few infomercials on during the day but at night they are featured on nearly every channel. Big Business knows that as consumers, our guard is down at night, so they capitalize by only feeding us shopping options.
"Shopping hangover" applies to infomercials as well as online shopping - since after around 11 p.m. people start to feel the need to buy everything they've ever thought about...and some things they haven't.
"Dude - when I checked my e-mail this morning and had 17 congratulatory messages from eBay, I was hit with the biggest shopping hangover! What did I DO last night?"