I don't think you're having a stroke either, but you may have temporomandibular joint problems (TMJ) or at least may be putting some unwanted pressure on one side of your jaw when you lie face-down. This is not as unusual as you might think, and TMJ is a frequent culprit in jaw tightness, jaw pain, facial numbness, etc. It could be as simple as your position while lying down, or it could be that you clench your jaw while sleeping (if you in fact sleep in that position). It could even be a combination of both.
You might want to bring this to the attention of a doctor or even a dentist. There are sometimes some fairly simple fixes if it is TMJ.
Hope this is helpful. Best of luck and please do stay in touch.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist