I drank 4-5 cups (5 oz) of coffee each workday for quite a few years now. Somehow I only associated the whole thing with work, so it didn't even occur to me to drink coffee on the weekends. The end result was two days of constant sleep with headaches and general grogginess, followed by a workweek of OK-ish performance.

I am now at week two in the process of quitting, because I'm getting increasingly concerned about being in the withdrawal zone as well as being "fully caffeinated". The first week was much worse than the second one. Hopefully I get back to my old self soon.