It is a classic example of pain caused due to faulty posture for a short period of time as in your case it was due to a position of neck in sleep... dont worry it is short term discomfort..... you can do hot water formentation to relieve tightness in the muscle... for a day avoid major physical activities which involves putting strain on neck like working on PCs or even riding a bike..... if pain persists after 2 days you can take OTC painkillers. Hope this Advice helps you.

Hey. It could be due to paraspinal muscle , stop exercise for time being ,MRI spine helps to rule out disc prolapse or inflammation at site of nerve root ,consult orthopedic doctor.