Which condition requires immediate medical attention in a patient on anticoagulants?

The sudden onset of a severe headache in a patient on anticoagulants requires immediate medical attention because it may indicate a serious condition such as a hemorrhagic stroke or intracranial bleed. Anticoagulants increase the risk of bleeding by preventing blood from clotting properly, which means that even a seemingly minor event can lead to significant and potentially life-threatening complications. This type of headache is often described as "the worst headache of my life," and other accompanying symptoms may include confusion, altered level of consciousness, or neurological deficits, all pointing to a possible emergency that mandates swift intervention.

In contrast, a persistent cough, moderate abdominal pain, or low-grade fever do not carry the same immediate threat of severe bleeding or acute life-threatening conditions, even though they may warrant medical evaluation. These symptoms can be attributable to a range of less critical health issues, which do not demand the same level of urgent intervention as a severe headache might in the context of anticoagulant therapy.