Is Long Term Use Of Nyquil Safe?

I have a deep chest cough and havent been sleeping well due to the cough. Ive been on zoloft for a couple months for panic disorder. Ive had no complications. I took Theraflu nighttime last night and slept very hard and didnt wake up coughing. I took Nyquil tonight... I feel fine alert and awake, is it safe to keep taking the Nyquil?