Caffeine problem? Feeling sick.?

Ever since I started my diet, I have been limiting the use of the unhealthy diuretics that are in some foods; aspirin, coffee, ect. And today, I had a bunch of caffeine. I used to be able to drink twelve cups of coffee and feel fine (if not a tad hyper) but I feel sick to my stomach. Every time I stand up I get sick and worry I may throw up. Is it the sudden caffeine or something else unrelated?