Sort of relating to The_Rck's suggestion - have you tried massage? It gooses the parasympathetic nervous system and is supposed to help (I say 'supposed to': research and anecdotal evidence are out there but I haven't read much, nor done it myself) with things like Fibro and MS. Not knowing what sort of chronic pain you're in or how localized/generalized it is I'm hesitant to suggest more specific types of modalities.

[Disclaimer: I'm a massage therapist.]