First, don't panic. This is becoming more and more routine. The IRS will send you a letter of explanation as to what kind of review and how long they expect it to take. Once the review has been completed and they agree with your return you will still receive your refund.
If they do not agree with your return after they review it, they can adjust the return based on information they have, and then will send you a letter explaining the adjustments and what they mean to your refund.