Does insomnia cause pupil dilation?

Not usually. Dilated pupils can occur as a side effect of various medications and several illicit drugs. Serious medical conditions such as serotonin syndrome can also cause this. Insomnia for a night or two would not usually result in dilated pupils. How long have you had insomnia? Have you been depressed or started a new medication? See your doctor to be sure and bring a list of all drugs, herbals takin.