Hi. You should go to your General Dentist (or a dentist specialising in TMD) and get fitted with an occlusal splint. This stops clenching and grinding. Prolonged clenching and grinding can actually cause TMD, cause it displaces the joints. Muscle relaxants. such as Valium, may aslo help the muscle spasms.
You may also have a back problem, because the muscle that leads to your jaw joint originates at the middle of your back. If this muscle is spasming, that would explain the neck and upper back soreness.
I hope this helps and puts you on the road of a pain free existance
Brooke :)
Most of your descriptions are consistent with temporomandibular disorder except weird head sensation. Seeing a tmj specialist is advised.