Oh, I see what you meant! I thought you were worried about permanent brain damage, because that's what most people are scared of. Sorry, my mistake.
If you're worried about paralysis, as in getting paralysed by breaking your neck, that's almost impossible to happen. There would have to be a significant amount of drop to break your neck. Neck spine fractures are extremely rare in suspension hanging suicides.
From what I see, using prescription antiemetics is essential. It's mentioned in every guide, including the PPH Handbook. Also, if you search on the forum, most people who try it without antiemetics fail. I definitely wouldn't try using SN on its own.
Regarding pain, SN looks peaceful. (I disagree, but this is the general opinion.) Apart from looks, I have no idea how it feels in reality. I mean, it isn't my method of choice, so I haven't researched it much. Hanging may look gruesome, but you lose consciousness quickly. It might be painful in the first few seconds, but it's definitely quick. The level of pain also depends on your pain tolerance. Some people say it isn't painful, and some say it's quite painful.
In terms of reliability, FSH is as reliable as it gets as long as you can ensure that your anchor point and rope don't break under your weight. It's also critically important that no one finds you for at least about 30 minutes (the longer the better). If you don't have the skills to create a good setup, other methods might be a better choice.