This description is the very definition of asthma, or of another respiratory or pulmonary issue.
Lying down is the TOUGHEST thing to do when you have asthma. It messes up your ability to exhale and the way your bronchioles respond.
It's normal NOT to be comfortable lying down if you have asthma or something like pneumonia.
Please, hit up a doctor, a PA, a Nurse Practitioner, and have your son tell them what's happening. Get him tested, see if he responds to simple meds.
I say this with lots of love and understanding...I've had asthma all my life but wasn't diagnosed until I got sick (with pneumonia, bronchitis, and laryngitis all at once) and almost died when I was 12. :/ Not a happy experience.