I haven't tried, so I don't personally know if it will hurt. Written accounts on the forum seem to vary. Everyone experiences pain different anyway and it's probably also relative to your situation. If you search for "documentation" here you should be able to find some timelines to get an idea of when people that CTB with SN usually lose consciousness. In general SN is said to be one of the most peaceful ways to go.
I feel for you. Suicide is a heavy topic and often scary. I don't wanna influence your decision in any way, but I do want you to know that SN has a pretty good shelf life. In case it's still too scary for you (at this point in time) you can reconsider as far as the SN goes. And if you change your mind last minute there is an antidote. I saw you replied to an older thread of someone that took SN and called emergency services and lived, so you probably know that.
I hope all the info and reading you've been doing will make you feel less scared