Should I be concerned?

[songlines]

For the past few years, at times I would wake up in the night, gasp for breath or it feels like I am gagging but when I sit up and cough immediately it goes away and I can breathe again and feel ok.  During the past year the times this happens has increased, it seems to happen especially if I lie on my left side.  I am 68 and 6 years ago I had a total check up in hospital of heart and lungs and all was normal.  I was reading today about something else and came across information on Paroxysmal Nocturnal Dyspnea and now I am a little worried that it may be heart failure! I will go and see my doctor tomorrow and clear it up.  Am I overreacting or what?