reality check

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An assessment to determine if one's circumstances or expectations conform to reality.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a check or review to make sure something is consistent, reasonable, etc.
• noun idiomatic a wake-up call, reminder

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an occasion on which one is reminded of the nature of things in the real world