Jasmine Willis, 17, developed a fever and began hyperventilating after downing seven double espressos while working at her family's sandwich shop.
The student, of Stanley, County Durham, was taken to the University Hospital of North Durham, where doctors confirmed she had overdosed on caffeine.
She has since made a full recovery and is now warning others about the dangers of excessive coffee drinking.
Ms Willis, who had thought the coffees were single measures, said the effects were so severe that she began laughing and crying for no reason while serving customers at the shop.
She developed a fever and began struggling to breathe after being sent home by her father.
"My nerves were all over the place.
"I was drenched. I was burning up and hyperventilating.
"I was having palpitations, my heart was beating so fast and I thought I was going into shock.
"I did not realise this could happen to you and I only hope other people learn from my mistake."
The teenager, who was allowed home after a few hours of observation, suffered side effects for days afterwards and now says she cannot stand the sight of coffee.
Her father Gary, who runs The Sandwich Bar in Stanley, said: "She did not realise she was drinking double measures.
"I have always stressed to my children the importance of moderation but Jasmine got caught out on this occasion."