Here is a list of some of the major culprits of a stiff neck. Avoid these and you can avoid having the dreaded stiff neck.
Not using a supportive pillow for your head and neck while sleeping. A flat pillow gives no support to the head and neck
Working on the computer all day with out taking breaks and having a bad posture while you are on the computer
Talking on the telephone all day at work with your head laterally bent to one side
Sleeping in an awkward position while sleeping can cause muscle spasm and muscle strain.
Meningitis: Although rare, if you stiff neck that is accompanied by a headache and a fever, there's a chance you may have meningitis. The pain tends to be quite severe with meningitis.
Whiplash from a car accident or trauma in the neck can cause a stiff neck. Not being able to move your head and neck in the proper range of motion stiffens your neck muscles
Using too many neck pillows at night. Using too many pillows under your neck can cause your neck to be put into a forward head posture, which puts more pressure on the back of the neck.
Falling asleep on the couch or wherever- Not sleeping with a good ergonomic pillow can put your head and neck into an awkward position.
Reading with your head bent in towards your chest for a prolonged period to time
Stress- it does the body no good? Many people carry much of their stress in the upper back and neck.
A Cold, Sinus Cold, Virus or Flu Like Symptoms tend to run your whole system down and unfortunately your neck can be affected. When neck pain is caused by flu, the neck and the rest of the body tend to ache all over, but there is no severe neck stiffness.