Dear Micmic,
SD is about desensitization of muscle to growth stimulus via lay-off from any intentional strenous activity.
But total inactivity is not recommended.
Postural muscles can go weak, bone can lose density. It still is recommended that one have a life while in SD. Vegging out in bed is perhaps, not ideal.
The use of Orphenadrine, Tizanidine etc (I do not know in great detail what these drugs do but from your message I gather they down-regulate sympathetic activity) is not necessary as long as you avoid strenous activity.
Your motor neurons are always excitatory, in that if stimulated they lead to contraction. The best way to relax them would be to not strain them i.e. don't lift weights, don't carry heavy luggage etc.
And if your voluntary muscles are in spasm, I'd recommend having a massage or two. Try to find an ART (Active Release Technique) practitioner if possible or at least one who is skilled in trigger-point therapy.
If you have access to such 'supplements', perhaps you would also have access to anabolic-injectable supplements? Those would do better in enhancing sensitivity of your muscles to growth stimuli.
All in all, as you have said it, it is a crazy idea to want to contemplate "The absolute SD: in bed 24/7, catheterized, intravenous feeding & strong sedatives". Considering drug side effects and loss of muscle and bone tone, don't do it.
Godspeed, and happy HSTing
