However in all cases if you decide to rest while poisoned, you may well never wake up, without any prior warning.
It seems it can happen in Daggerfall classic too, so from that point of view that may not be considered a bug. (Classic seems to give more visual feedback though: vital indicators are correctly updated as your condition changes. I don't know if you can click exit and avoid death if you're fast enough).
However if you start fast traveling, the game will warn that you may be about to die, so that's not consistent.
I don't know if that's realistic, I guess some poisons are painless or at least not painful enough to wake you up, or trigger some coma or paralysis first, so you may very well never wake up from poisoning.
After all those considerations, ways this could be handled:
- leave behavior as is. As said before it's not consistent, and can frustrate players, but matches classic and may very well be realistic;
- match fast travel behavior: if you try to rest while poisoned, you'll get a warning that you may be about to die, and can cancel your action;
- When "You feel somewhat bad." happens, unconditionally or conditionally wake up. That's the option I like the best, but may be harder to implement. Conditional wakeup gives player more options, but again I don't know if that's realistic for all poisons.