Based on my personal experience, full suspension hanging may "pinch" your neck muscles and that will hurt (I tried doing that with a rope in my hand a few minutes ago). For this reason I recommend you "prepare" your neck by pulling the rope upwards and checking if your neck muscles are ok. If it's all good you should be good to go.
I won't sugar coat it and lie about it being painless, but you will lose consciousness fairly quickly anyway. I recommend you check the thread I posted about how full suspension hanging feels like according to several people that tried it. It doesn't seem too traumatic. And I personally believe death to be always unpleasant, regardless of method.
I recommend you stretch your neck muscles beforehand, to minimize any pinching that may happen (if it happens).
And about the forest thing, yeah, sounds like a good plan to me if you find a good tree to hang yourself from.