Hello,
First its important to know what Forward head posture is.
For every inch your head moves "forwards", the head "gains" 10 pounds in weight, as far as the muscles in your upper back and neck are concerned, as they have to work harder to keep the head (chin) from dropping forwards onto your chest. This forces the muscles that raise the chin to remain in constant contraction, putting pressure on the 3 Suboccipital nerves. This can cause headaches at the base of the skull, and even mimic sinus headaches!
An anterior positioning of the cervical spine is caracteristic of forward head posture. Forward head posture may may make it more difficult to perform exercises with the bar in front of head or neck. Evaluate neck position at night since elevating head too high with additional pillows may act as a continuous neck stretch throughout the evening exacerbating the forward head posture.
The head should sit directly over the shoulders. The head weighs about the same as a bowling ball, so holding it forward, or out of alignment puts strain on the neck and upper back muscles and spinal tissues. When spinal tissues are under a significant load for a long period of time they begin to deform and remodel structurally and can become permanent. Forward head posture also has been shown to decrease the curvature in the neck leading to disc compression, damage and arthritis. This is why forward head posture takes a long time to correct. Some of the symptoms associated with forward head posture are fatigue, headaches, pain, carpals tunnel, TMJ and even fibromyalgia, just to name a few. Forward head posture has been linked to many neck and upper back conditions.
Also have a look at www.causeof.org/posture_fhp.htm
I hope that it was of some help.
Cheers.