State involuntary muscle contraction of the neck, its main symptom is headache and neck pain, this is caused by poor position at bedtime, or some movement that we did wrong.
The treatments for this are usually some home remedies, or painkillers, but mainly rest.
Heat in the neck and back, recommend showering with water as hot as your body supports
Massages in the affected area, only recommended by an expert.
Exercises in the neck, for this it is recommended to be under the shower but soft and slow exercises, because it can injure more the muscle.
These are the first remedies that should be done, if the discomfort does not improve in 3 days we should visit a doctor.