My two year-old son was taking Omnicef for Sinusitis. After about three days on it, he became very restless and started waking in the night. This continued throughout the ten-day course of the drug. It continued throughout the next week, as well. When he stopped taking Omnicef, he became very irritable and aggressive. It took about three days for the "withdrawl" symptoms to stop. He is finally back to normal.