Hi Im A 25 Year Old Male , I Was

Hi im a 25 year old male , i was at a family party last night and had quite a few drinks , i woke up on the sofa this morning with the usually bad head , stiff neck and sore back , during the day ive noticed every time i bend over or look down my left nostril strats dripping this yellow watery fluid , smells and feels like a nose bleed but its just yellow water ? What is it ?