The Lord is said to speak to us in dreams, but it's kind of hard to tell if they're real or not until they come true. Where discernment comes in has to do with whether or not the "prophet" is giving the information in the name of "another God" or is saying that the prophecy came from the one true God when it really didn't. The "tehcnicality" here, though, is what if the person speaking of dreams they feel are prophetic _thinks_ they're coming from the One True God?
Numbers 12:6 --
he said, “Listen to my words:
“When there is a prophet among you, I, the LORD, reveal myself to them in visions,
I speak to them in dreams."
But there's also this:
Deuteronomy 17-21 -- "The LORD said to me: “What they say is good. 18 I will raise up for them a prophet like you from among their fellow Israelites, and I will put my words in his mouth. He will tell them everything I command him. 19 I myself will call to account anyone who does not listen to my words that the prophet speaks in my name. 20But a prophet who presumes to speak in my name anything I have not commanded, or a prophet who speaks in the name of other gods, is to be put to death.”
21 You may say to yourselves, “How can we know when a message has not been spoken by the LORD?” 22 If what a prophet proclaims in the name of the LORD does not take place or come true, that is a message the LORD has not spoken. That prophet has spoken presumptuously, so do not be alarmed."