"Crash"
From Wikipedia...This increase in the number of the adenosine receptors (i.e. caffein
intake) makes the body much more sensitive to adenosine, with two primary
consequences. First, the stimulatory effects of caffeine are substantially
reduced, a phenomenon known as a tolerance
adaptation. Second, because these adaptive responses to caffeine
make individuals much more sensitive to adenosine, a reduction in caffeine
intake will effectively increase the normal physiological effects of adenosine,
resulting in unwelcome withdrawal
symptoms in tolerant users.
Because adenosine, in part,
serves to regulate blood pressure by causing vasodilation, the increased effects
of adenosine due to caffeine withdrawal cause the
blood vessels of the head to dilate, leading to an excess of blood in the head
and causing a headache and nausea.
Reduced catecholamine activity may cause feelings of
fatigue and drowsiness. A reduction in serotonin levels when caffeine use is stopped can cause anxiety,
irritability, inability to concentrate and diminished motivation to initiate or
to complete daily tasks; in extreme cases it may cause mild depression.
Together, these effects have come to be known as a "crash".
In large amounts, and especially over
extended periods of time, caffeine can lead to a condition known as caffeinism. Caffeinism usually
combines caffeine dependency with a
wide range of unpleasant physical and mental
conditions including nervousness,
irritability, anxiety, tremulousness, muscle twitching (hyperreflexia),
insomnia, headaches, respiratory alkalosis and heart
palpitations. Furthermore, because caffeine increases the
production of stomach acid, high usage over time can lead to peptic ulcers,
erosive esophagits, and (blah blah blah)
There are four caffeine-induced psychiatric
disorders recognized by the Diagnostic and Statistical Manual of
Mental Disorders, Fourth Edition: caffeine intoxication, caffeine-induced
anxiety disorder, caffeine-induced sleep disorder, and caffeine-related disorder
not otherwise specified (NOS).
Oh crap.