caffeine withdrawal causes headache and dry mouth and general unease, even after just one day. Especially if you're used to huge amounts.
What are the symptoms of caffeine withdrawal?
Regular caffeine consumption reduces sensitivity to caffeine. When
caffeine intake is reduced, the body becomes oversensitive to
adenosine. In response to this oversensitiveness, blood pressure drops
dramatically, causing an excess of blood in the head (though not
necessarily on the brain), leading to a headache.
This headache, well known among coffee drinkers, usually lasts from
one to five days, and can be alleviated with analgesics such as
aspirin. It is also alleviated with caffeine intake (in fact several
analgesics contain caffeine dosages).
Often, people who are reducing caffeine intake report being irritable,
unable to work, nervous, restless, and feeling sleepy, as well as
having a headache. In extreme cases, nausea and vomiting has also been
reported.
from
http://www.faqs.org/faqs/caffeine-faq/