You can try cuddling him for a bit longer after he closes his eyes to ensure that he is in deeper sleep before placing him back on the bed.
It sounds like your son has night terrors.
Night terrors are common in young children and may occur when they are overly fatigued, stressed or sick.
Maybe you can also try out some methods from this page: http://sg.theasianparent.com/how-to-help-your-child-sleep-through-the-night/
http://kidshealth.org/parent/medical/sleep/terrors.html#
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