My tendonitis came after a strenuous hiking weekend (12 hours out, then 17 back by a tougher route) in boots with no arch support. The physical therapist ordered me to go out and buy the highest heels I dared to wear and wear them most of the day for a week or so. That leaves the achilles tendon pretty much immobilized. I don't recall it taking all that long to heal -- not long enough to really learn to balance on high heals -- but this was years ago so my memory may have de-traumatized itself somewhat.