I am considering the same. I read
this article (PDF attached) and there were no reported deaths in the time period of the study. The most serious reported symptom was a coma. Based off the symptoms of a slow heart rate, low blood pressure, and coma, it seems it would be a relatively painless(?) death. Don't take my word on that, but I didn't see anything serious, like seizures, reported in the study. You would probably have to take quite a huge dose if you planned on using this as a method.