Painless methods is that of CO poisoning but it is not the fastest. I don't think any other method of suicide is painless however, suicide using chloroform or general anesthetics may be painless because you will faint and won't realize what happened to you. They are definitely not the fastest. However, the fastest method of suicide listed in this blog is that of cyanide poisoning. Apart from this one, one that I did not put in the list of top 20 suicide methods is the method of using a firearm. Gunshot on your head. It will not take time but yes some, pain will be there!