Błędnie: You should be more careful. Ignoring the gripe and not staying in bed with fever may lead to heart problems in the future. Poprawnie: You should be more careful. Ignoring the flu and not staying in bed with fever may lead to heart problems in the future.
"Gripe" oznacza 'problem', 'zagadnienie', 'skargę'. 'Grypa' to po angielsku "flu".