What you are describing is a very common problem. Typically what happens is that the muscles of the neck that run up and down the sides of the spinal column (called the paraspinal muscles) become strained and go into spasm, usually just as the result of 'sleeping funny.' Other causes of neck muscle strain
can include working intensely at a computer all day long, or similar activities that involve a stooped posture.
Spasm of the muscles of the neck, called paraspinal muscle spasm, can be very painful, and it typically also causes a sensation of stiffness and difficulty turning the neck from side to side.
Fortunately, the condition does tend to resolve on its own over time, however it may take days to week to resolve completely. Therefore, the fact that you are still having symptoms 4 days out is not at all surprising.
Regardless, I would advise discussing this issue with your family doctor
. Initial treatment of this condition could include working on maintaining good posture, applying heat or cold to the area for pain relief, and taking standard anti inflammatory medications like ibuprofen or naproxen. More serious treatments may also be in order.
Good luck, and again, please speak to your doctor soon!