Question

why our eyes become red when we fell sleepy

Answer 1

HEY DEAR......!!!

We've all experienced red, bloodshot eyes from time to time, affecting one or both eyes. Red eye is caused by swollen or dilated blood vessels on the sclera, the white outer surface of the eye. ... In other cases, a red eye may cause no irritation at all.

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Answer 2

there are blood vessels on the part of eye attached to it . when sleeping hormone send signals to CNS the motor neuron pass the information to those vessels to increase flow of blood there then we have a sensation of sleeping