I never had a nose bleed until I started doing 12hr+ legs on the triple 7.
Frequent use of a saline nasal spray has prevented a recurrence.
Regarding inflight fainting spells.
Often times dehydration can cause blood pressure to drop to the point that a person can pass out usually after sitting for long periods and then quickly standing.
The importance of staying hydrated for both passengers and crew cannot be stressed enough. Typically, the thirst sensation is minimal even with the extremely low humidity levels. A conscious effort, therefore, is required to maintain proper body hydration during prolonged flights.