Diphenhydramine may cause sedation, dizziness, tinnitus (ringing in the ears), fatigue (excessive tiredness), ataxia (lack of muscle coordination), blurred vision, diplopia (double vision), euphoria (feeling of great happiness or well-being), nervousness, and tremors (muscle shaking). Gastrointestinal effects include epigastric distress, nausea and vomiting, which may be reduced by taking diphenhydramine with meals. Other side effects include dryness of mouth and mucous secretions, palpitation (rapid and irregular heart beat), urinary tract dysfunction, and severe allergic reactions such as difficulty of breathing and swelling of the face, neck, tongue or throat. Phenylpropanolamine may cause sudden, persistent, severe headache, nervousness, restlessness, insomnia/sleeplessness, dizziness, anxiety (feeling of uneasiness), confusion, high blood pressure, palpitation, chest tightness, tremor, agitation, irritability, aggressiveness (particularly in young children), nausea, and blurred vision.