Based on the English glosses, {mIS} "be confused, mixed up" just means any sort of mental confusion where you don't comprehend or understand what's going on. {rel} "be dazed, bewildered" suggests a stronger sort of mental impairment, where you're confused enough that you can't even think straight and don't know what to say or do. (Dictionary.com uses "stupefied" to define "dazed", for instance.)
Assuming I'm correct, one glib way to think about it might be:
If your response to something is "Could you explain that again? I really don't follow," you're {mIS}.