Wow ,everything you,ve explained sounds alot like something I went through years ago ,allthough not quite as serious , pretty bad.
I was a heroin addict for afew years when I was younger and the withdrawls where alot like what you explained...constant muscle pain,feels like your bones hurt and the constant anxiety was the worst pain I've ever felt.
Last time I kicked in LA county jail...I was detoxing from heroin(alot of it)xanax(alot) and methadone(not alot).
I have to say the xanax was worse then the heroin...it made me sick for about 2-3 months,grinding my teeth,couldn't sleep or eat for about 2 weeks...felt like I lost my mind and was never coming back...seeing things,hearing things...horrible things,the worst you can imagine...
I know what some of you are thinking,Why do you still smoke pot if your a recovering heroin addict...well I'll tell ya...I quit several times only to relapse and start all over again.The more I did this the more I realized that if I didn't smoke bud I would go straight to heroin if I relapsed,but if I got stoned when I would start craving the smack I would more often then not be to high or to lazy or just content,so I would be less inclined to go through all the trouble of going out and commiting a felony.
Ha Ha
Or the weed would make me think things through and I would deside not to do it for my own sake.
So for me cannabis as saved my life in everyway possible...
My brain is alittle fryed from all the differant chemicals I've put in my body so I need it to feel normal(calm).
I'm proud to say I don't even crave that crap anymore and the only chemical in my body now is THC!!!

If you want to call it a chemical( I wouldn't)