Welcome to the community Guialdereti! I hope you stay with us to see the game come to life.
I recommend reading Design Journal 4, this is based around Incapacitation and Spirit walking, I'll throw the link in down the bottom for your convenience.
however to offer a brief answer, Spirit walking is when you have to do the proverbial "ghost run" back to your body that so many games choose to implement, however SBS adds another flair to it which will add (what i hope to be) quite a lot of importance in each spirit walk where it gradually becomes harder and harder for you to find your body based on your Spirit and Character age. This is seen as through a silver thread connecting your spirit to your body.
I believe you are able to "wake up" a short distance away from where you were incapacitated, however the exact distance is yet to be confirmed by the devs.
I actually asked a similar question about permanent damage after death, and I was told that limbs an such will remain intact once you get back to your body. As for poison and such, I can't find anything, so I don't think its yet been confirmed or even really touched upon. However I imagine that would depend on the types of poison or diseases in play, as well as the Biome your in if there are any outside sources at play.
I hope I was able to help, and once again, welcome to the community! We look forward to hearing you in Discord
Link to the Dev Journal; https://chroniclesofelyria.com/blog/348/Design-Journal-4-Incapacitation-Spirit-Walking-and-Permadeath