Are you saying the back left side of your head or the back left side of your neck?
I had pain in my neck itself from the ballooning, that went away within a few days on the right side but lasted a few weeks on the left. I've also had 'back of the skull' headaches and venoplasty brought one on the day of the procedure but it went away quickly. I can't remember the last time I had one, which is great because I used to have that all the time. The 'back of the skull' headache might have something to do with emissary veins:
The findings were more subtle on the left side. I can discern no clues (except some possible puddling of contrast media within the cusp of a normal appearing venogram). The small amount of opacification of a condylar emissary vein is within normal appearance. It is interesting that the patient has not posterior skull base head and neck ache. I strongly suspect that this headache is due to distension of the posterior cervical veins. chronic-cerebrospinal-venous-insufficiency-ccsvi-f40/topic10680-6885.html