I agree with the above poster. There's a much higher likelihood of being found by someone. I've read of people being unconscious for 5 hours before finally dying from SN. Since there's no way to ascertain how long your body will take to succumb to the SN, it leaves a potentially hours long window for someone to find you slumped over in the car.
Also, there have been reports of people getting up or walking around even after ingesting the SN, so who knows if you may try to get out of the car or even drive. That's a fairly improbable scenario, but it's plausible and could be highly dangerous.
I'm so sorry life has brought you to this point