Several of my children have FAS and while that's it's not autism some characteristics of FAS are hyperactivity, NO impulse control and a very low pain threshold. Those last two symptoms make these children very dangerous to themselves because they honestly think (actually they don't spend a lot of time in thought about it) that it might be fun to jump over the bannister and roll down two flights of stairs. When my daughter started getting up at night and wandering around we had the same fears that you have so we eventually started locking her in. With our bedroom right next to hers we could hear if she needed us in the night and she was safe.