People with a high caffeine intake can experience withdrawal effects when consumption ceases, but it there is also some empirical support to suggest that even persons consuming no more than two cups of coffee a day can suffer from clinically significant headaches, anxiety and fatigue if caffeine is withdrawn from their daily diet.
Moreover, the stimulant effect of caffeine is short-lived and it is not uncommon for the drinker to experience a considerable slump in energy following the intitial 'boost' provided by a lovely frothy cappuccino...