Complex sentence: Paroxysmal nocturnal dyspnoea (or dyspnea) refers to attacks of severe shortness of breath and coughing that generally occur at night, usually awakening the person from sleep, and may be quite frightening.
Split into simpler sentences: Paroxysmal nocturnal dyspnoea (or dyspnea) refers to attacks of severe shortness of breath and coughing that generally occur at night. It usually awakening the person from sleep, and may be quite frightening.