It might be Cervical spondylitis... its acute symptoms would be pain behind neck shooting to one or both of your arm or to back of your head.
Next Steps
You should consult an orthopaedician.. give rest to neck.. do not move it abruptly.. if you have desk work or any other work requiring you to look down.. avoid it immediately.. give hot pack to affected area. take rest.
Health Tips
Do not use pillows while lying down/ sleeping. If feeling dizziness in head immediately go for consultation and start with exercises.