A feeling one gets whilst he has a head cold, With a runny nose and head ache, and after he or she gets out of the shower all of the mucus and pressure has been released thus making the person feel like he is all better.
Mom:Oh you look like you have a cold
Son:Naw, Trust me I feel alot better now that I have taken a shower
Mom:So how do you feel?
Mom:You must have been Shower High