This type of night time shortness of breath can be caused by several different things. If you were a little older, or complaining of other symptoms, I would raise the possibility that you may have a problem with your heart. People with heart failure have trouble lying flat at night because they often wake up with fluid in their lungs which feels like they are suffocating. If you have had a recent significant decrease in your exercise tolerance, or if you started noticing fluid collection in your feet and ankles, then this is a possibility. If you are not experiencing this, then I think in someone your age heart failure should be lower on the list of possibilities. Other possibilities include night-time panic attacks, nightmares or night terrors. A sleep study may be able to shed some light on that.
If you have any of the above symptoms that suggest you could have a heart issue, then you should schedule an appointment with a cardiologist
. If this is not the case (and I am guessing it isn't since you did not mention these symptoms), then I suggest that you schedule an appointment with your primary care physician
. Press him or her to explain to you what possible problems you may have given your other past medical history. Hopefully, you will get to the bottom of it soon.