What Causes Neck Pain?
neck strain.NSAID, muscle relaxant.hot compression
I went through the query and understood your concern.
Since it started with neck pain after sleep with no rashes or clinical features of cold or sinusitis, the most probable cause is neck muscle strain. You should take NSAID like aceclofenac with muscle relaxants like chlorzoxazone/ tizanidine twice daily for 3-5 days based on the responce along with hot compression. This will help you. Along with this,physiotherapy will be helpful.
If your pain does not relieve in 3 - 5 days then scanning is required to diagnose if any other problem.
I hope this information helps you. Feel free to ask for any further queries. I will be glad to answer them.
Wish you good health and faster recovery.