It is unlikely that melatonin or zopiclone would directly cause shortness of breath unless you have an existing respiratory condition like severe sleep apnea or respiratory failure. However, it is possible for zopiclone to affect your sleep quality which may indirectly contribute to breathing difficulties. It is recommended to consider reducing the dose of these medications, especially since they are intended for occasional use rather than long-term use. If the shortness of breath persists, it is advisable to consult a healthcare professional for a thorough evaluation to determine the underlying cause, which could be related to anxiety or other factors.