1. Anything prolonged and painful. I can envisage far too many gruesome and absurd things here, so in terms of the conventional, I guess burning is bad enough.
2. Not settling down with someone, not doing anything worthwhile
3. Yes, though I'm much more scared of for instance getting a terminal illness and knowing I will die than the notion of just suddenly dying, as I believe I would be none the wiser in the latter case..
4. Yes. I never want my existence/consciousness in some form to end.