Nose bleeds can occur in the morning because of trauma to the nose during sleep. Also, when we lay down, blood circulates with a higher pressure in the upper body (as opposed to a higher pressure in the lower body when we stand up), potentially causing a nose bleed. Nose bleeds are very common in the morning hours and can occur for unknown reasons.
In cold months, dry heat is the most common cause for nose bleed. humidifier can help to prevent nosebleed.