hot bath (whether you use radox or not isn't relevant really - the heat of the water will ease the muscle pain, not the actual soap). or get a neck support pillow that can be heated in the microwave and wrap that around your neck (or a hot water bottle). Also try tiger balm (similar to deep heat etc). ibuprofen is also available in gel form and can be applied straight to the affected area for a quicker relief from the pain. is it whiplash type pain? if persists, see doctor for painkillers or possible referral for physio (depending how severe it is and how long you've had it).