Death wobbles are from just the right (wrong?) combination of factors. Fork stiffness,fork and frame geometry, small issues like headset adjustment and quality, you (someone else on the bike probably will not be able to reproduce the wobbles), One thing that often makes them far worse is fear and tensing up, especially your hands and grip. A way to stop the wobbles is to place your knee against the top tube. If that isn't enough, use your other knee as well. I find being underdressed makes my best bike a lot worse.