Breakdown of Ich darf die Allergie nicht vergessen.
ich
I
nicht
not
vergessen
to forget
dürfen
to be allowed to, may
Questions & Answers about Ich darf die Allergie nicht vergessen.
Doesn't dürfen mean "to be allowed to"? Why does the translation say "must not"?
You are right that dürfen means "to be allowed to." However, when it is negated (nicht dürfen), it means "to not be allowed to." In English, the most natural way to express that you are strictly not allowed to do something is "must not." Watch out: if you used nicht müssen instead, it would mean "do not have to," which completely changes the meaning!
Why does nicht go right before vergessen instead of earlier in the sentence?
When you want to negate the main action in a sentence that has a modal verb, nicht gets pushed to the end, right in front of the infinitive verb. Here, you are negating the entire action of forgetting, so it locks into place just before vergessen.
Could I put nicht right after darf, like "Ich darf nicht die Allergie vergessen"?
You should avoid that unless you are making a specific contrast. Putting nicht directly in front of a specific noun (like one with die, der, or das) sounds like you are saying "I must not forget the allergy (but rather I must not forget the appointment)." To just state a simple negative fact, nicht belongs after the specific object.
Why is it "die Allergie" and not "der" or "den" here?