Some of you really think too hard on this. Lmfao, dang. Such detail.
I'd say burning to death or falling. Like 9/11 for example when people jumped out the windows, or falling off a water tower, skyscraper, etc. That's scary to me. Seeing yourself fall, with your only bought being "I'm so fucked".
The worst way to die would be getting buried in the ground up to your neck with just your having your head out of the ground. And have thousands of flesh eating ants dumped on your head and being left there until they kill you. It will take up to 3 days before you die by the way.