My brother just experienced a nosebleed accompanied by dizziness, the nosebleeding stopped but he says he still feels strange. What is wrong?

Probably anxious. Sudden nosebleeds can be anxiety laden events especially if spontaneous, without provocation, & since it always appears much more blood is lost than actually happens many get nervous & may even feel sick or faint but not from blood loss- from the emotion of the event. Having said that, if your brother actually had a MAJOR nosebleed then, he should drink some fluids and rest. If no better see doc.