I used to get this quite frequently when I lived in the heart of downtown Toronto and had an extreme drinking (alcoholic) habit. It scared me half to death the

I used to get this quite frequently when I lived in the heart of downtown Toronto and had an extreme drinking (alcoholic) habit. It scared me half to death the first few times it happened, then it was just annoying once I realized what it was. Moved out of Toronto and stopped drinking heavily and I don't get them at all anymore. I remember being woken up constantly at 2/3/4/5am to police/ambulence sirens and car horns. So psychological stress (as wikipedia suggests) was most definitely a factor in my having had this imho. Just my 2 cents.