Final answer:
Jordan is experiencing withdrawal from caffeine, a substance that can create dependence and cause withdrawal symptoms when use is abruptly stopped.
Step-by-step explanation:
Jordan is experiencing withdrawal symptoms after discontinuing her coffee consumption cold turkey. Caffeine, a stimulant found in coffee, can lead to physical and psychological dependence, and abrupt cessation of intake can cause various withdrawal symptoms, such as severe lethargy. This occurs because the body has to adjust to the absence of the substance it has become used to functioning with.
Withdrawal symptoms are common in the context of a substance that the body has become accustomed to, and these symptoms are typically opposite of the effects of the drug. When Jordan stopped taking caffeine, her central nervous system experienced a downshift in stimulation, which can manifest as lethargy or fatigue - a stark contrast to the alertness caffeine usually induces.