Why do your eyes get crusty when you sleep?

Why do we get red eyes when we are sleep deprived and when we consume too much alcohol ?

• - While other sensory organs connected to brain are fine or atleast looking fine outwardly, Why these eyes become red?  Is  this because the blood vessels in sclera swells and since because it is  white it is visible ? if so, why blood vessels swell ? > sorry, idk about anatomy, so if i am fundamentally wrong, pls correct me. Thanks a lot :D

• Answer:

  Red eyes result from a dilation or enlargement of the blood vessels in  the white part of the eye (sclera). Just like a rash or injury on the other parts  of your body, this is your body's way of addressing the problem at  hand. They force more blood into the irritated or injured area in order  to provide more oxygen and to remove as many of the toxins as they can. usually this is due to an increase in Nitric Oxide by the parasympathetic system, causing the vasodilation.This answer is not a substitute for professional medical advic...