Use of nosebleeds to denote arousal? In several episodes of Assassination Classroom (animated version), characters develop spontaneous nosebleeds seemingly in response to becoming sexually aroused.  This occurs with a number of male characters, though I can recall at least one instance where it happens to a female character as well.  

Here's an example on Youtube:

https://www.youtube.com/watch?v=sKNRnL6E64Q

Is this a common trope in anime, or something that's unique to Assassination Classroom?  And in either case, is there any rational explanation behind using this seemingly bizarre method of depicting arousal?
This is a common trope in anime. Many examples of it can be seen on Dragon Ball with Master Roshi:



Source: https://www.youtube.com/watch?v=y0-Ep3UI2SI [potentially suggestive content]

According to AnimeNewsNetwork, it is a long-standing Japanese folk belief.