The mental fog is not directly related to the neck issue. Inflammation is usually the issue. Some therapists (chiros, osteopaths, PTs, even some massage therapists) can reduce the tension with gentle traction and mobilization or gentle spinal manipulation or massage or pressure/trigger point or myofacial release the muscle tension. There is not one size fits all treatment. What is more important is finding the right therapist and therapy that works for you. In the experience of many, only 1 in 20 who say they can help can actually help.

Plus, you need to be disciplined with head and neck posture and even icing to help keep the inflammation down. Reducing the inflammation can increase blood flow that can improve quality of sleep and help with the mental fog.